Magnetic recording and reproducing apparatus

ABSTRACT

In the present invention, with respect to a convex-concave structure necessary for respective functions of a servo area in a perpendicular magnetic recording medium, a specification of configuration and magnetic property of a convex-concave magnetic layer of the perpendicular magnetic recording medium is set so as to overcome a demagnetizing field that accelerates thermal fluctuation. Therefore, in a magnetic recording and reproducing apparatus using the perpendicular magnetic recording medium having servo tracking signals at convex portions of the magnetic layer formed in a convex-concave pattern, it is possible to suppress degradation of the servo signals caused by the thermal fluctuation to thereby ensure a stable servo function over the long term.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic recording and reproducingapparatus including a magnetic recording medium having a magneticrecording layer formed in a predetermined convex-concave pattern on asubstrate and thus having so-called servo areas and information dataareas (a magnetic recording medium of a discrete type) and a magnetichead for detecting servo signals on the magnetic recording medium andrecording and reproducing information data on and from the medium.

2. Description of the Related Art

Improvement in areal recording density of magnetic recording mediumssuch as hard disks has conventionally been achieved by techniques ofboth (1) improving the linear recording density and (2) improving thetrack density. In order to achieve further and higher densification infuture, it is necessary to improve the areal recording density based onthe foregoing both techniques.

With respect to improving the track density, there have been raisedproblems of processing limitation about magnetic heads, side-fringe orcrosstalk caused by expansion of magnetic fields of magnetic heads, andso forth, and therefore, it can be said that the improvement in arealrecording density by progressing the track-density increasing techniquefor magnetic heads, which is merely an extension of the conventionalimprovement technique, has reached the limit.

On the other hand, as a technique of improving the linear recordingdensity, reduction in layer thickness and higher coercive forces havebeen achieved in conventional longitudinal magnetic mediums. However, interms of further and higher densification of the mediums and stabilityof recording magnetization against thermal fluctuation, attention hasbeen paid to perpendicular magnetic recording mediums.

Under these circumstances, as a technique of improving the arealrecording density and supplementing the higher track densification ofthe magnetic heads, there have been proposed magnetic recording mediumsof a discrete track disk type in which a recording layer is formed in apredetermined convex-concave pattern. For example, JP-A-H11-328662discloses a magnetic recording medium in which predetermined convex andconcave portions are formed on a substrate and a perpendicular magneticlayer in the form of a single layer is formed along the convex andconcave portions.

A reduction in spacing is necessary for accomplishing an increase inrecording density. However, there is a possibility that theconvex-concave shape of the recording layer may impede the stable flyingcharacteristic of a magnetic head and thus cause a problem of head crashor the like. From this point of view, JP-A-H10-222944 discloses arecording medium in which the convex-concave shape changes in a trackwidth direction for the purpose of achieving the flying stability of amagnetic head.

Further, JP-A-2000-195042 proposes a discrete type magnetic recordingmedium in which concave portions in the convex-concave shape are filledwith a nonmagnetic material or another material for ensuring thestability in flying characteristic of a magnetic head.

On the other hand, JP-A-H06-111502 discloses a technique that defines arelationship among the width of each of rectangular tracking servo burstpatterns formed by a convex-concave structure on a longitudinalrecording medium, the track pitch, and the read width of a reproducinghead.

In general, on a magnetic recording medium used in a magnetic diskdrive, servo areas necessary for a magnetic head to perform tracking arerecorded by a servo track writer.

The servo area generally includes an ISG (Initial Signal Gain) portion,an SVAM (SerVo Address Mark) portion, a Gray code portion, a burstportion, and a pad portion which are in the form of various magneticpatterns for exhibiting predetermined functions, respectively.

The magnetic patterns of the burst portion are each recorded with awidth equal to that of one track in a radial direction of the magneticrecording medium. On the other hand, the ISG portion, the SVAM portion,the Gray portion, and the pad portion are each recorded continuously inthe disk radial direction over several tracks or entirely.

The recent increase in recording density of magnetic recordingapparatuses has been remarkable and, following it, the sizes ofrecording bits recorded on magnetic recording mediums have been reduced.Consequently, a reduction in size of magnetic grains is also requiredfor ensuring high S/N ratios. In this regard, it is said that, inconnection with the longitudinal magnetic mediums which have been widelyused, when a value of KuV/kT, i.e. a ratio between a magnetic grainmagnetization energy KuV (Ku: magnetic anisotropy constant, V: magneticgrain volume) and an ambient temperature thermal energy kT (k:Boltzmann's constant, T: absolute temperature), becomes smaller thanabout 60 as a general standard, the so-called phenomenon of thermalfluctuation occurs wherein the magnetization fluctuates with certainprobability due to disturbance of the thermal energy and decreases withthe passage of time.

In view of this, in order to increase the magnetization energy of themagnetic grains, attention has been paid to the perpendicular magneticrecording mediums that can increase the thickness thereof even at highdensity.

The perpendicular magnetic recording medium becomes more stable in itsmagnetization and thus becomes stronger against the thermal fluctuationas the density increases, while, since a diamagnetic field serving toreduce the magnitude of the magnetization increases at low recordingdensity, i.e. in an area where the bit length is large, the influence ofthe thermal fluctuation tends to be accelerated to reduce the recordingmagnetization.

Therefore, the area that is most affected by the thermal fluctuation isthe servo area where servo signals are recorded at relatively lowrecording density.

Once recorded, the servo signal is normally not recorded again by themagnetic head, and therefore, it is susceptible to the influence ofthermal fluctuation over the long term so that there may arise a problemthat the servo signal is degraded due to a reduction in recordingmagnetization, resulting in reduction of the tracking servo signalquality.

In view of such a problem, JP-A-H11-25402 discloses a technique wherein,in recording magnetization of tracking servo signals in a perpendicularmagnetic recording medium having no convex-concave structure, the bitlengths of the servo signals are set such that a maximum demagnetizationfield at the time of magnetization saturation in recording bits becomessmaller than a coercive force of a recording layer, and whereinrelational expressions for the setting are derived.

In this proposed technique, the servo signals are continuously arrangedwhile perpendicular magnetizations M of rectangular bits are alternatelyinverted as shown in figures of this publication, and therefore, adiamagnetic field Hd generated at a certain bit is reduced in itsdiamagnetic field due to magnetic fields H from the most adjacent bits.Particularly, the diamagnetic field theoretically becomes zero in aboundary between the bits and it is thus considered that the valueapproximate to the saturation magnetization is ensured in the vicinityof ideal magnetization transition.

However, as shown in JP-A-H06-111502, in case of the discrete track diskhaving the convex-concave structure, rectangular recording bits arenormally arranged at intervals of one bit in a burst portion which is inthe convex-concave shape of a magnetic recording layer corresponding tothe servo patterns. Further, rectangular bits each elongate in the diskradial direction are arranged at intervals of one bit in an ISG portion,an SVAM portion, and a Gray code portion.

In the discrete track disk where the magnetic recording layer isprocessed into the convex-concave structure as described above, as isdifferent from the system in which the inverted magnetizations arecontinuously recorded on the perpendicular magnetic medium as describedin JP-A-H11-25402, convex portions, where servo signals are recorded, ofthe magnetic recording layer are completely isolated from each other sothat there exist no such most adjacent bits that are inverselymagnetized and serve to weaken a diamagnetic field. Further, those bitsdistanced from each other by one bit length are magnetized in the samedirection so that the effect of reducing the diamagnetic field is hardlyexpected and they rather serve to increase the diamagnetic field.

Therefore, there is a demand for design guidelines for the magneticrecording layer convex portions for the servo signals that are formedcompletely isolated from each other.

On the other hand, when forming the convex-concave structure of aperpendicular magnetic recording layer (magnetic layer), it is possibleto shorten the operation time and reduce the production cost as thedepth of a concave portion is set smaller. Therefore, it can be saidthat the manner of forming a convex-concave magnetic layer withoutcompletely removing the magnetic layer in the depth direction and offilling concave portions with a nonmagnetic material is a desirable wayin terms of simplifying the process and reducing the operation cost.

However, if the convex-concave shape of the magnetic layer is determinedwithout taking a scheme into consideration, there may arise a problemthat the servo signal output decreases in relation to the magnitude ofthe depth of the concave portion of the magnetic layer. Particularly,there is a possibility that various degradation modes may be caused byparameters of the convex-concave structure of the perpendicular magneticrecording layer (magnetic layer), the depth of the concave portionthereof, and further, magnetic properties, applied herein, of theperpendicular magnetic recording layer (magnetic layer) in the servoarea. Therefore, with respect to servo tracking signals at the convexportions of the magnetic layer formed in the convex-concave pattern, ithas been difficult to ensure a sufficient long-term reliability againstthermal fluctuation.

The present invention has been made under these circumstances and has anobject to provide a magnetic recording and reproducing apparatusincluding a perpendicular magnetic recording medium having servotracking signals at convex portions of a magnetic layer formed in aconvex-concave pattern, wherein the magnetic recording medium cansuppress degradation of the servo signals caused by thermal fluctuationto thereby ensure a stable servo function over the long term.

SUMMARY OF THE INVENTION

For accomplishing the foregoing object, the invention of a first groupand the invention of a second group have been made, respectively. Amagnetic recording and reproducing apparatus in the invention of each ofthe first and second groups comprises a perpendicular magnetic recordingmedium of a discrete type having a data information recording portion(data area) and a servo information portion (servo area) for tracking,wherein a specification of a convex-concave structure of the servo areaof the medium is set taking magnetic properties thereof intoconsideration so that the influence of a diamagnetic field thataccelerates thermal fluctuation of the perpendicular magnetic recordingmedium can be reduced in the servo area of the medium which is mostaffected by the thermal fluctuation of the medium. Particularly, withrespect to the convex-concave structure necessary for respectivefunctions of the servo area, the specification of configuration andmagnetic property of the convex-concave magnetic layer of theperpendicular magnetic recording medium is set so as to overcome thediamagnetic field that accelerates the thermal fluctuation.

SUMMARY OF THE INVENTION OF FIRST GROUP

The invention of the first group is configured as follows.

Specifically, according to one aspect of the present invention, there isprovided a magnetic recording and reproducing apparatus comprising amagnetic recording medium having a data information recording portionand a servo information portion for tracking, and a magnetic head fordetecting servo information of the servo information portion andrecording and reproducing data information on and from the datainformation recording portion, wherein the servo information portion isformed by a convex pattern of a magnetic layer formed in a predeterminedconvex-concave pattern and a nonmagnetic material is filled inside aconcave pattern, the servo information portion comprising a burstportion where burst signals for tracking are recorded, the burst portionis formed by disposing at predetermined positions magnetic layers in theform of convex portions where the burst signals are recorded, and when alength of the magnetic layer in the form of the convex portion in atrack circumferential direction is given as L′1, a length thereof in atrack width direction (track radial direction) is given as W′1, a wholethickness of the magnetic layer in a region of the convex portion isgiven as t, an interval in the track width direction (track radialdirection) between the magnetic layers in the form of the convexportions adjacent to each other is given as W′2, an interval thereof inthe track circumferential direction is given as L′2, a thickness of themagnetic layer remaining under a concave portion is given as δ, and acoercive force, a saturation magnetization, and a coercive forcesquareness ratio in a direction perpendicular to the film plane of themagnetic layer in the form of the convex portion are given as Hc, Ms,and S*, respectively, a specification of the burst portion is set sothat the coercive force squareness ratio S* takes a value of 0.8 or moreand a relationship of a first inequality is satisfied, the firstinequality given as${{Hc} \cdot S^{*}} > {{Ms}\quad\left( {{4\arctan\frac{L^{\prime}1\quad W^{\prime}1}{t\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + t^{2}}}} - {4\arctan\frac{L^{\prime}1\quad W^{\prime}2}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}2^{2}} + t^{2}}}} + {4\arctan\frac{L^{\prime}1\quad W^{\prime}1}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{L^{\prime}1\quad\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{t\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + t^{2}}}}} \right)}$

In the magnetic recording and reproducing apparatus of the presentinvention, it may be arranged that when a coercive force, a remanentmagnetization, and a coercive force squareness ratio in the directionperpendicular to the film plane of the magnetic layer in the form of theconvex portion are given as Hc, Mr, and S*, respectively, thespecification of the burst portion is set so that the coercive forcesquareness ratio S* takes the value of 0.8 or more and a relationship ofa second inequality is satisfied, the second inequality given as${{Hc} \cdot S^{*}} > {{Mr}\quad\left( {{4\arctan\frac{L^{\prime}1\quad W^{\prime}1}{t\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + t^{2}}}} - {4\arctan\frac{L^{\prime}1\quad W^{\prime}2}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}2^{2}} + t^{2}}}} + {4\arctan\frac{L^{\prime}1\quad W^{\prime}1}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{L^{\prime}1\quad\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{t\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + t^{2}}}}} \right)}$

In the magnetic recording and reproducing apparatus of the presentinvention, it may be arranged that the magnetic layer in the form of theconvex portion has a substantially rectangular parallelepiped shape.

In the magnetic recording and reproducing apparatus of the presentinvention, it may be arranged that the sum of L′1 and L′2 is set as awavelength of frequency of a servo signal.

According to another aspect of the present invention, there is provideda magnetic recording and reproducing apparatus comprising a magneticrecording medium having a data information recording portion and a servoinformation portion for tracking, and a magnetic head for detectingservo information of the servo information portion and recording andreproducing data information on and from the data information recordingportion, wherein the servo information portion is formed by a convexpattern of a magnetic layer formed in a predetermined convex-concavepattern and a nonmagnetic material is filled inside a concave pattern,the servo information portion comprising belt-like convex portions eachextending in a track radial direction (track width direction), thebelt-like convex portion has a belt-like shape having a length L′1 in atrack circumferential direction and a length in the track radialdirection that is 100 times or more the length L′1, and when a wholethickness of the magnetic layer in a region of the belt-like convexportion is given as t, an interval in the track circumferentialdirection between the magnetic layers in the form of the belt-likeconvex portions adjacent to each other is given as L′2, a thickness ofthe magnetic layer remaining under a region of a concave portion isgiven as δ, and a coercive force, a saturation magnetization, and acoercive force squareness ratio in a direction perpendicular to the filmplane of the magnetic layer in the form of the belt-like convex portionare given as Hc, Ms, and S*, respectively, a specification of thebelt-like convex portion is set so that the coercive force squarenessratio S* takes a value of 0.8 or more and a relationship of a firstinequality is satisfied, the first inequality given as${{Hc} \cdot S^{*}} > {{Ms}\quad\left( {{4\arctan\frac{L^{\prime}1}{t}} + {4\arctan\frac{L^{\prime}1}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)}} + {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{t}}} \right)}$

In the magnetic recording and reproducing apparatus of the presentinvention, it may be arranged that when a coercive force, a remanentmagnetization, and a coercive force squareness ratio in the directionperpendicular to the film plane of the magnetic layer are given as Hc,Mr, and S*, respectively, the specification of the belt-like convexportion is set so that the coercive force squareness ratio S* takes thevalue of 0.8 or more and a relationship of a second inequality issatisfied, the second inequality given as${{Hc} \cdot S^{*}} > {{Mr}\quad\left( {{4\arctan\frac{L^{\prime}1}{t}} + {4\arctan\frac{L^{\prime}1}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)}} + {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{t}}} \right)}$

In the magnetic recording and reproducing apparatus of the presentinvention, it may be arranged that the magnetic layer in the form of thebelt-like convex portion has a belt-like rectangular parallelepipedshape.

In the magnetic recording and reproducing apparatus of the presentinvention, it may be arranged that recording of servo signals in theservo information portion is carried out at a time by applying amagnetic field perpendicular to the plane of the magnetic layers of themagnetic recording medium in a DC magnetic field.

SUMMARY OF THE INVENTION OF SECOND GROUP

The invention of the second group is configured as follows.

Specifically, according to one aspect of the present invention, there isprovided a magnetic recording and reproducing apparatus comprising amagnetic recording medium having a data information recording portionand a servo information portion for tracking, and a magnetic head fordetecting servo information of the servo information portion andrecording and reproducing data information on and from the datainformation recording portion, wherein the servo information portion isformed by a convex pattern of a magnetic layer formed in a predeterminedconvex-concave pattern and a nonmagnetic material is filled inside aconcave pattern, the servo information portion comprising a burstportion where burst signals for tracking are recorded, the burst portionis formed by disposing at predetermined positions magnetic layers in theform of convex portions where the burst signals are recorded, themagnetic layer in the form of the convex portion has a first and asecond substantially trapezoidal shape in a track width direction (trackradial direction) and in a track circumferential direction,respectively, and when an upper side corresponding to an upper surfaceof the magnetic layer in the form of the convex portion is given as W1,a lower side corresponding to a bottom side of the magnetic layer in theform of the convex portion which is extended to reach a base (a lowerside corresponding to a bottom side of the magnetic layer in the form ofthe convex portion defined by extending the first trapezoidal shape) isgiven as W2, and an interval between the adjacent lower sides W2 isgiven as W3 with respect to the first trapezoidal shape in the trackwidth direction, an upper side corresponding to the upper surface of themagnetic layer in the form of the convex portion is given as L1, a lowerside corresponding to a bottom side of the magnetic layer in the form ofthe convex portion which is extended to reach a base (a lower sidecorresponding to a bottom side of the magnetic layer in the form of theconvex portion defined by extending the second trapezoidal shape) isgiven as L2, and an interval between the adjacent lower sides L2 isgiven as L3 with respect to the second trapezoidal shape in the trackcircumferential direction, a whole thickness of the magnetic layer in aregion of the convex portion (a distance from the upper side to thelower side of the magnetic layer in the form of the convex portion) isgiven as t, a thickness of the magnetic layer remaining under a concaveportion is given as δ, and a coercive force, a saturation magnetization,and a coercive force squareness ratio in a direction perpendicular tothe film plane of the magnetic layer in the form of the convex portionare given as Hc, Ms, and S*, respectively, a specification of the burstportion is set so that the coercive force squareness ratio S* takes avalue of 0.8 or more and a relationship of a first inequality issatisfied, the first inequality given as${{Hc} \cdot S^{*}} > {{Ms}\quad\left\{ {{4\arctan\frac{{L1}\quad{W1}}{t\sqrt{{L1}^{2} + {W1}^{2} + t^{2}}}} + {4\arctan\frac{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\left( {{W2} - {W1}} \right)}} \right)}{{t\left( {t - {2\delta}} \right)}\sqrt{\begin{matrix}{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} - {W1} - {W3}} \right)} -} \right.} \\{\left. {\delta\left( {{W2} - {W1}} \right)} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}\end{matrix}}}} - {4\arctan\frac{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{- {tW2}} + {\delta\left( {{W2} - {W1}} \right)}} \right)}{{t\left( {t - {2\delta}} \right)}\sqrt{\begin{matrix}{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{tW2} - {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} +} \\\left( {t\left( {t - {2\delta}} \right)} \right)^{2}\end{matrix}}}} + {4\arctan\frac{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)}{{t\left( {t - {2\delta}} \right)}\sqrt{\begin{matrix}{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} +} \right.} \\{\left. {\delta\left( {{W2} - {W1}} \right)} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}\end{matrix}}}} - {4\arctan\frac{\left( {{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)}{{t\left( {t - {2\delta}} \right)}\sqrt{\begin{matrix}{\left( {{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} +} \\{\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}\end{matrix}}}} + {4\arctan\frac{\left( {{L2} + {2{L3}}} \right)\left( {{W2} + {2{W3}}} \right)}{t\sqrt{\left( {{L2} + {2{L3}}} \right)^{2} + \left( {{W2} + {2{W3}}} \right)^{2} + t^{2}}}}} \right\}}$

In the magnetic recording and reproducing apparatus of the presentinvention, it may be arranged that when a coercive force, a remanentmagnetization, and a coercive force squareness ratio in the directionperpendicular to the film plane of the magnetic layer in the form of theconvex portion are given as Hc, Mr, and S*, respectively, thespecification of the burst portion is set so that the coercive forcesquareness ratio S* takes the value of 0.8 or more and a relationship ofa second inequality is satisfied, the second inequality given as${{Hc} \cdot S^{*}} > {{Mr}\quad\left\{ {{4\arctan\frac{{L1}\quad{W1}}{t\sqrt{{L1}^{2} + {W1}^{2} + t^{2}}}} + {4\arctan\frac{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\left( {{W2} - {W1}} \right)}} \right)}{{t\left( {t - {2\delta}} \right)}\sqrt{\begin{matrix}{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} - {W1} - {W3}} \right)} -} \right.} \\{\left. {\delta\left( {{W2} - {W1}} \right)} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}\end{matrix}}}} - {4\arctan\frac{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{- {tW2}} + {\delta\left( {{W2} - {W1}} \right)}} \right)}{{t\left( {t - {2\delta}} \right)}\sqrt{\begin{matrix}{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{tW2} - {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} +} \\\left( {t\left( {t - {2\delta}} \right)} \right)^{2}\end{matrix}}}} + {4\arctan\frac{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)}{{t\left( {t - {2\delta}} \right)}\sqrt{\begin{matrix}{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} +} \right.} \\{\left. {\delta\left( {{W2} - {W1}} \right)} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}\end{matrix}}}} - {4\arctan\frac{\left( {{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)}{{t\left( {t - {2\delta}} \right)}\sqrt{\begin{matrix}{\left( {{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} +} \\{\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}\end{matrix}}}} + {4\arctan\frac{\left( {{L2} + {2{L3}}} \right)\left( {{W2} + {2{W3}}} \right)}{t\sqrt{\left( {{L2} + {2{L3}}} \right)^{2} + \left( {{W2} + {2{W3}}} \right)^{2} + t^{2}}}}} \right\}}$

In the magnetic recording and reproducing apparatus of the presentinvention, it may be arranged that a relationship of W2>W1 and L2>L1 issatisfied.

In the magnetic recording and reproducing apparatus of the presentinvention, it may be arranged that the sum of L2 and L3 is set as awavelength of frequency of a servo signal.

According to another aspect of the present invention, there is provideda magnetic recording and reproducing apparatus comprising a magneticrecording medium having a data information recording portion and a servoinformation portion for tracking, and a magnetic head for detectingservo information of the servo information portion and recording andreproducing data information on and from the data information recordingportion, wherein the servo information portion is formed by a convexpattern of a magnetic layer formed in a predetermined convex-concavepattern and a nonmagnetic material is filled inside a concave pattern,the servo information portion comprising belt-like convex portions eachextending in a track radial direction (track width direction), thebelt-like convex portion has a trapezoidal shape, in a trackcircumferential direction, with an upper side L1 corresponding to anupper surface of the magnetic layer in the form of the belt-like convexportion and a lower side L2 corresponding to a bottom side of themagnetic layer in the form of the belt-like convex portion which isextended to reach a base (a lower side corresponding to a bottom side ofthe magnetic layer in the form of the belt-like convex portion definedby extending the trapezoidal shape) and has a length in the track radialdirection which is 100 times or more a length of L2, and when aninterval between the lower sides L2 of the adjacent belt-like convexportions is given as L3, a whole thickness of the magnetic layer in aregion of the belt-like convex portion (a distance from the upper sideto the lower side of the magnetic layer in the form of the belt-likeconvex portion) is given as t, a thickness of the magnetic layerremaining under a concave portion is given as δ, and a coercive force, asaturation magnetization, and a coercive force squareness ratio in adirection perpendicular to the film plane of the magnetic layer in theform of the belt-like convex portion are given as Hc, Ms, and S*,respectively, a specification of the belt-like convex portion is set sothat the coercive force squareness ratio S* takes a value of 0.8 or moreand a relationship of a first inequality is satisfied, the firstinequality given as${{Hc} \cdot S^{*}} > {{Ms}\quad\left\{ {{4\arctan\frac{L1}{t}} + {4\arctan\frac{{tL2} - {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} + {4\arctan\frac{{L2} + {2{L3}}}{t}}} \right\}}$

In the magnetic recording and reproducing apparatus of the presentinvention, it may be arranged that when a coercive force, a remanentmagnetization, and a coercive force squareness ratio in the directionperpendicular to the film plane of the magnetic layer in the form of thebelt-like convex portion are given as Hc, Mr, and S*, respectively, thespecification of the belt-like convex portion is set so that thecoercive force squareness ratio S* takes the value of 0.8 or more and arelationship of a second inequality is satisfied, the second inequalitygiven as${{Hc} \cdot S^{*}} > {{Mr}\quad\left\{ {{4\arctan\frac{L1}{t}} + {4\arctan\frac{{tL2} - {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} + {4\arctan\frac{{L2} + {2{L3}}}{t}}} \right\}}$

In the magnetic recording and reproducing apparatus of the presentinvention, it may be arranged that a relationship of L2>L1 is satisfied.

In the magnetic recording and reproducing apparatus of the presentinvention, it may be arranged that recording of servo signals in theservo information portion is carried out at a time by applying amagnetic field perpendicular to the plane of the magnetic layers of themagnetic recording medium in a DC magnetic field.

In the magnetic recording and reproducing apparatus of the presentinvention, it may be arranged that the servo information portion isformed in the predetermined convex-concave pattern and the nonmagneticmaterial for providing a discrete function is filled in the concaveportions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view showing an overall shape of adisk-shaped magnetic recording medium in the invention of a first group;

FIG. 2 is an enlarged schematic view of a small portion surrounded by arectangle in FIG. 1;

FIG. 3 is a sectional view conceptually showing a preferred embodimentof the magnetic recording medium in the invention of the first group;

FIG. 4 is a schematic perspective view showing a structure of aperpendicular magnetic recording layer in the invention of the firstgroup;

FIG. 5 is a schematic perspective view showing a structure of aperpendicular magnetic recording layer in the invention of the firstgroup;

FIG. 6 is a schematic perspective view of a magnetic recording andreproducing apparatus in the invention of the first group;

FIG. 7 is a diagram showing a magnetization-magnetic field curve of themagnetic recording medium in the invention of the first group;

FIG. 8 is a plan view for explaining one example of another servopattern;

FIG. 9 is a schematic plan view showing an overall shape of adisk-shaped magnetic recording medium in the invention of a secondgroup;

FIG. 10 is an enlarged schematic view of a small portion surrounded by arectangle in FIG. 9;

FIG. 11 is a sectional view conceptually showing a preferred embodimentof the magnetic recording medium in the invention of the second group;

FIG. 12 is a schematic perspective view showing a structure of aperpendicular magnetic recording layer in the invention of the secondgroup;

FIG. 13 is a schematic perspective view showing a structure of aperpendicular magnetic recording layer in the invention of the secondgroup;

FIG. 14 is a schematic perspective view of a magnetic recording andreproducing apparatus in the invention of the second group;

FIG. 15 is a diagram showing a magnetization-magnetic field curve of themagnetic recording medium in the invention of the second group; and

FIG. 16 is a plan view for explaining one example of another servopattern.

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, the invention of a first group and the invention of asecond group will be described in order.

Description will be first given in detail about an embodiment of theinvention of the first group (corresponding to FIGS. 1 to 8).

[Description About the Invention of First Group]

A magnetic recording and reproducing apparatus of the present inventioncomprises a magnetic recording medium having data information recordingportions and servo information portions for tracking, and a magnetichead for detecting servo information of the servo information portionsand recording and reproducing data information on and from the datainformation recording portions.

At the outset, an example of a schematic structure of the magneticrecording and reproducing apparatus will be described with reference toFIG. 6 in order to understand the overall structure of the apparatus.

Description of Example of Schematic Structure of Magnetic Recording andReproducing Apparatus

FIG. 6 is a perspective view showing a schematic structure of themagnetic recording and reproducing apparatus being one preferred exampleof the present invention.

In this figure, a magnetic recording medium 1 is a disk-shapedperpendicular magnetic recording medium and is rotationally driven by aspindle motor 2.

Further, in order to read and write data relative to the magneticrecording medium, a recording and reproducing magnetic head 5 isprovided at the tip of a swing arm 4 extending radially inward towardthe center of the medium from its outer peripheral side. The swing arm 4is swung by a voice coil motor 3 so that, for example, the magnetic head5 can be positioned at a given track based on servo signals detected bythe magnetic head 5.

The magnetic head 5 has a recording element and a reproducing element. Asingle-pole head of a main-pole excitation type, for example, is used asthe recording element, while, a GMR (Giant MagnetoResistance effect)head, for example, is used as the reproducing element. A TMR (TunnelingMagnetoResistance effect) head or the like may be used instead of theGMR head.

Description of Magnetic Recording Medium

Now, the structure of the magnetic recording medium will be described.

FIG. 1 is a schematic plan view showing the overall shape of thedisk-shaped magnetic recording medium 1 used in the present invention,and FIG. 2 is an enlarged schematic view of a small portion 100surrounded by a rectangle in FIG. 1. FIG. 2 conceptually illustratesmainly a servo information portion 90 being an area where servo signalsare recorded, and data information recording portions 80 each in theform of a group of data tracks for recording and reproduction.

FIG. 3 is a sectional view conceptually illustrating a preferredembodiment of the magnetic recording medium in the present invention.FIG. 3 substantially corresponds to a sectional view taken along linea-a in FIG. 2.

In FIG. 1, although not illustrated, a plurality of data track groupsfor recording and reproduction are concentrically disposed/formed on adisk substrate.

Further, servo signal regions (servo information portions 90: thoseportions drawn as radial lines in FIG. 1) are radially formed extendingoutward from the center of the disk. That is, a so-called sector servosystem is employed wherein the disk surface is divided into sectors.Servo information is recorded in each of the servo information portions90 of the magnetic recording medium.

The structure of the servo information portion 90 will be described indetail. As shown in FIG. 2, the servo information portion 90 (so-calledservo area) comprises an ISG (Initial Signal Gain) portion 91, an SVAM(SerVo Address Mark) portion 92, a Gray code portion 93, a burst portion94, and a pad portion 95.

The ISG portion 91 is in the form of a continuous pattern provided forexcluding influences of unevenness in magnetic property of a magneticfilm (magnetic layer) of the magnetic recording medium and in flyingamount of the magnetic head and is continuously formed in the trackradial direction. While reproducing the ISG portion 91 by the magnetichead, the gain of a servo demodulation circuit is determined by anautomatic gain control (AGC) so as to correct variation in output causedby the magnetic recording medium or the magnetic head. The automaticgain control (AGC) that performs such an operation is turned off whenthe SVAM portion 92 existing in the servo area is detected, andstandardizes the reproduction amplitude existing in the later burstportion 94 by the amplitude of the ISG portion 91.

The Gray code portion 93 is recorded with information about respectivetrack numbers and a sector number.

The burst portion 94 is in the form of patterns for providing preciseposition information necessary for the magnetic head to perform accuratetracking to the track position. These patterns are normally composed ofa combination of first bursts 94 a and second bursts 94 b each equallystraddling a center line that defines the track pitch between theadjacent tracks and a combination of third bursts 94 c and fourth bursts94 d each located at a position offset from the first and second burstsby half the track pitch. As shown in FIG. 2, the patterns of the burstportion 94 are each normally recorded with a width equal to that of onetrack in a radial direction of the magnetic recording medium.

The pad portion 95 is in the form of a pattern provided for absorbing adelay of a demodulation circuit system so that clock generation can bemaintained while the servo demodulation circuit reproduces the servoarea.

The ISG portion 91, the SVAM portion 92, and the pad portion 95 are eachrecorded continuously in the disk radial direction, while, the Gray codeportion 93 is recorded over several tracks or more in the disk radialdirection.

Referring now to FIG. 3, description will be given about an example of apreferred section structure of the magnetic recording medium. FIG. 3 canbe understood as, for example, the sectional view taken along line a-ain FIG. 2.

As shown in FIG. 3, the magnetic recording medium comprises a substrate15, an orientation layer 14 formed on the substrate 15, a soft magneticlayer 11 formed on the orientation layer 14, an intermediate layer 12formed on the soft magnetic layer 11, perpendicular magnetic recordinglayers 10 and nonmagnetic layers 20 corresponding to convex portions andconcave portions, respectively, of the convex-concave shape formed onthe intermediate layer 12, and a protective layer 13 formed on thelayers 10 and 20. In the formation of the convex-concave pattern informing the perpendicular magnetic recording layers 10 of the presentinvention, the magnetic layer is not completely removed in the depthdirection so that the magnetic layer remains at a thickness of about δunder the concave portions (residual magnetic layers 10 a).

Specifically, the servo information portion in the present invention isformed by a convex pattern (perpendicular magnetic recording layers 10)of the magnetic layer formed in the predetermined convex-concavepattern, and a nonmagnetic material is filled inside a concave pattern.

The ratio (δ/t) of the thickness δ of the residual magnetic layer 10 aremaining under the concave portion relative to a thickness t of theperpendicular magnetic recording layer 10 corresponding to the magneticlayer at the convex portion is set to 0.6 or less, preferably 0.1 to0.6, and more preferably 0.2 to 0.4. If this value exceeds 0.6 (thegroove becomes shallow), magnetization becomes liable to be recorded atthe concave portion due to a magnetic field from a recording head and anundesired magnetic field becomes strong from the once-recordedmagnetization so that a noise component increases. On the other hand, ifthis value becomes less than 0.1 (the groove becomes deep), it becomesdifficult to perform predetermined accurate etching and further itbecomes extremely difficult to perform filling of the nonmagneticmaterial and flattening of the surface after the formation of thegroove, resulting in difficulty of stable manufacture.

As the substrate 15, use is preferably made of a glass substrate, anNiP-coated aluminum alloy substrate, an Si substrate, or the like. Asthe orientation layer 14, use can be made of, for example, anantiferromagnetic material such as PtMn for applying an anisotropicmagnetic field to the soft magnetic layer 11 in the track widthdirection. Alternatively, use may be made of a nonmagnetic alloy forcontrolling the orientation.

As the soft magnetic layer 11, there can be cited a CoZrNb alloy, anFe-based alloy, a Co-based amorphous alloy, a soft magnetic/nonmagneticmultilayer film, soft magnetic ferrite, or the like.

The intermediate layer 12 is provided for controlling a perpendicularmagnetic anisotropy and a crystal grain size of the perpendicularmagnetic recording layers formed on the intermediate layer 12, and aCoTi nonmagnetic alloy or Ru, for example, is used therefor.Alternatively, use may be made of a nonmagnetic metal, an alloy, or alow-permeability alloy that works similarly.

As the convex-portion perpendicular magnetic recording layer 10(including the residual magnetic layer 10 a), use is preferably made ofa medium in which ferromagnetic grains of CoPt or the like are containedin a matrix in an SiO₂ oxide-based material, a CoCr-based alloy, an FePtalloy, a Co/Pd-based artificial lattice type multilayer alloy, or thelike.

As a material of the concave-portion nonmagnetic layer 20, use is madeof a nonmagnetic oxide such as SiO₂, Al₂O₃, TiO₂, or ferrite, a nitridesuch as AlN, or a carbide such as SiC.

Normally, the protective layer 13 in the form of a carbon thin film orthe like is formed on the surfaces of the convex-portion perpendicularmagnetic recording layers 10 and the nonmagnetic layers 20 filled in theconcave portions by the use of the CVD method or the like.

The formation of the perpendicular magnetic recording layers 10 and thenonmagnetic layers 20 based on the convex-concave pattern (the formationof the so-called discrete type medium) is carried out by, for example,etching a perpendicular magnetic recording layer, formed in a constantthickness, into a predetermined convex-concave shape, then sputteringSiO₂ corresponding to an etching depth to fill etched concave portions.Thereafter, SiO₂ excessively deposited on the perpendicular magneticrecording layer is removed by applying oblique ion-beam etching or thelike while rotating the medium, thereby flattening the whole surface ofthe medium.

Setting of Specification of Servo Area (Servo Information Portion)

It can be said that the main part of the present invention resides inthat a specification of configuration and magnetic property of aconvex-concave magnetic layer of a perpendicular magnetic recordingmedium is set so as to suppress degradation of a servo signal to therebyensure a stable servo function over the long term in a servo area (servoinformation portion) formed by a convex pattern of the convex-concavemagnetic layer which is formed in a predetermined convex-concave pattern(the magnetic layer of a so-called inner excavation type).

Hereinbelow, with respect to the magnetic recording layers (magneticlayers) having the convex structures for the respective functions in theservo area, description will be separately given about (1) the burstportion 94 (94 a to 94 d) forming a first group that requiresconsideration of lengths in both the track radial direction (disk radialdirection) and the track circumferential direction and (2) the ISGportion 91, the SVAM portion 92, the Gray code portion 93, and the padportion 95 forming a second group that requires consideration of lengthsonly in the track circumferential direction because lengths in the trackradial direction (disk radial direction) are extremely longer than thelengths in the track circumferential direction.

(1) Description of First Group in the Invention of First Group

The convex shape satisfying a required condition of the first groupcorresponds to the shape of the burst portion 94 as described before. Asshown in a schematic perspective view of FIG. 4, the burst portion 94 isformed by disposing at predetermined positions the perpendicularmagnetic recording layers 10 in the form of convex portions wheremagnetizations of burst signals are recorded in the same direction, andeach perpendicular magnetic recording layer 10 in the form of the convexportion has substantially rectangular shapes (including square shapes)in the track width direction and in the track circumferential direction,respectively. That is, the convex portion of the magnetic layer has asubstantially rectangular parallelepiped shape (including a cubicshape).

Further, in the present invention, the residual magnetic layers 10 aremain under the concave portions. The meaning of leaving the residualmagnetic layers 10 a under the concave portions resides in reduction ofprocesses for the processing of the concave portions and reduction ofthe depth of the concave portions which leads to easiness of the surfaceflattening thereafter. However, the depth should be set to a value thatcan prevent a signal from the magnetic layer under the concave portionfrom affecting the servo area or the data area.

Incidentally, illustration of the nonmagnetic layers filled in theconcave portions is omitted in the figure for better understanding ofthe shape of the perpendicular magnetic recording layer 10 in the formof the convex portion.

When, in FIG. 4, the length of the magnetic layer at the convex portion(perpendicular magnetic recording layer 10) in the track circumferentialdirection is given as L′1, the length thereof in the track widthdirection (track radial direction) is given as W′1, the whole thicknessof the magnetic layer in a region of the convex portion (including alower part of the convex shape as shown in FIG. 4) is given as t, theinterval between the magnetic layers at the convex portions(perpendicular magnetic recording layers 10) adjacent to each other inthe track width direction (track radial direction) is given as W′2, theinterval between the magnetic layers at the convex portions(perpendicular magnetic recording layers 10) adjacent to each other inthe track circumferential direction is given as L′2, the thickness ofthe magnetic layer remaining under the concave portion (residualmagnetic layer 10 a) is given as δ, the magnetic properties in adirection perpendicular to the film plane of the convex-portion magneticlayer (perpendicular magnetic recording layer 10) are assumed to exhibitan M (magnetization)-H (magnetic field) characteristic as shown in FIG.7, and a coercive force, a saturation magnetization, and a coerciveforce squareness ratio in the direction perpendicular to the film planeof the convex-portion magnetic layer (perpendicular magnetic recordinglayer 10) are given as Hc, Ms, and S*, respectively, it is necessary todetermine a configuration of the convex portion (including the magneticlayer under the concave portion) and set magnet properties of theperpendicular magnetic recording layer so that the coercive forcesquareness ratio S* takes a value of 0.8 or more and a relationship ofan inequality (1′) below is satisfied, thereby determining aspecification of the burst portion.

For the respective parameters, units shown in tables of later-describedexamples are used.

The coercive force squareness ratio S* is a value determined by theslope of a tangent line at a point −Hc of the M-H curve shown in FIG. 7which has been corrected by a diamagnetic field, and a value of Mr, andis defined as S*=Hc′/Hc. Hc′ represents a value of the coercive force ata point of intersection between the tangent line at the point −Hc of theM-H curve and a straight line of M=Mr in the second quadrant as shown inFIG. 7. Note that “corrected by a diamagnetic field” represents that anapplied magnetic field is corrected, with respect to a value ofmagnetization caused by the applied magnetic field, by the use of adiamagnetic field generated by the product of the magnetization and adiamagnetic field coefficient in the direction perpendicular to theperpendicular magnetic recording layer, thereby deriving the M-H curve.$\begin{matrix}{{{Hc} \cdot S^{*}} > {{Ms}\quad\left( {{4\arctan\frac{L^{\prime}1\quad W^{\prime}1}{t\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + t^{2}}}} - {4\arctan\frac{L^{\prime}1\quad W^{\prime}2}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}2^{2}} + t^{2}}}} + {4\arctan\frac{L^{\prime}1\quad W^{\prime}1}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{L^{\prime}1\quad\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{t\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + t^{2}}}}} \right)}} & \left( 1^{\prime} \right)\end{matrix}$

The expression on the right side of the inequality (1′) represents themagnitude of a diamagnetic field when a saturation magnetization Ms isrecorded at the magnetic layer formed by the convex-concave patternshown in FIG. 4. It has been found that, by setting a value Hc′(=Hc·S*), i.e. the product of a coercive force Hc and a coercive forcesquareness ratio S*, to be greater than a numerical value of thedemagnetizing field serving to reduce the recorded magnetization, it ispossible to suppress inversion of the magnetization recorded at theconvex portion to thereby suppress degradation of a servo signal so thatthe long-term stability can be achieved.

In this event, it is necessary that the value of the coercive forcesquareness ratio S* be set to 0.8 or more (preferably 0.85 to 1.0, andmore preferably 0.9 to 1.0). When the value of the coercive forcesquareness ratio S* becomes less than 0.8, the squareness ratio of theM-H curve is decreased, and therefore, there arises a disadvantage thatwhile the demagnetizing field is being applied to the magnetization inthe perpendicular magnetic recording layer, the magnetization can bemore easily inverted due to an external magnetic field and thermalfluctuation of the magnetization. In case of the discrete pattern in theso-called discrete medium, the influence of the demagnetizing fieldbecomes extremely large as compared with the conventional continuousmedium.

The length of the sum of L′1 and L′2 is equal to a wavelengthcorresponding to a frequency of the burst patterns. W′1 and W′2 are eachnormally set equal to a track width of the perpendicular magneticrecording medium.

When deriving the foregoing inequality (1′) using a magnetic layer modelformed by the convex-concave pattern shown in FIG. 4, the followingpoints were considered.

Specifically, in case of the discrete medium, the adjacent bits areisolated from each other as different from the continuous medium, andtherefore, the value of the demagnetizing field Hd was derived withrespect to a demagnetizing field in one specific pattern. In order toderive the representative magnitude, the demagnetizing field was derivedby superimposing, at the center of the rectangular structure, magneticfields generated from magnetic charges induced by a perpendicularmagnetization M at upper and lower surfaces of the pattern and magneticfields generated from upper and lower surfaces of the magnetic layerlocated under the concave portions (four portions along the sides of theconvex portion) innerly excavated so as to surround the rectangularstructure of the convex-portion magnetic layer.

Further, when a remanent magnetization of the magnetic layer formed bythe convex-concave pattern is given as Mr, it is necessary to determinea configuration of the magnetic layer formed by the convex-concavepattern and set magnet properties of the perpendicular magneticrecording layer so that a relationship of an inequality (2′) below issatisfied, thereby determining a specification of the burst portion withrespect to the magnetic layer formed by the convex-concave pattern whichis the same as that in the inequality (1′).

For the respective parameters, the units shown in the tables of thelater-described examples are used.

The points considered when deriving the inequality (2′) are the same asthose in case of the inequality (1′). $\begin{matrix}{{{Hc} \cdot S^{*}} > {{Mr}\quad\left( {{4\arctan\frac{L^{\prime}1\quad W^{\prime}1}{t\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + t^{2}}}} - {4\arctan\frac{L^{\prime}1\quad W^{\prime}2}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}2^{2}} + t^{2}}}} + {4\arctan\frac{L^{\prime}1\quad W^{\prime}1}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{L^{\prime}1\quad\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{t\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + t^{2}}}}} \right)}} & \left( 2^{\prime} \right)\end{matrix}$

The expression on the right side of the inequality (2′) represents themagnitude of a demagnetizing field in the state where saturationrecording is carried out and the magnetization becomes a remanentmagnetization Mr at the magnetic layer formed by the convex-concavepattern shown in FIG. 4. It has been found that, by setting a value Hc′(=Hc·S*), i.e. the product of a coercive force Hc and a coercive forcesquareness ratio S*, to be greater than a numerical value of thedemagnetizing field serving to reduce the recorded magnetization, it ispossible to suppress inversion of the magnetization recorded at theconvex-portion magnetic layer to thereby suppress degradation of a servosignal caused by a reduction in recording magnetization so that thelong-term stability can be achieved. In this event, as described before,it is necessary that the value of the coercive force squareness ratio S*be set to 0.8 or more (preferably 0.85 to 1.0, and more preferably 0.9to 1.0). When the value of the coercive force squareness ratio S*becomes less than 0.8, the squareness ratio of the M-H curve isdecreased, and therefore, there arises a disadvantage that while thedemagnetizing field is being applied to the magnetization in theperpendicular magnetic recording layer, the magnetization can be moreeasily inverted due to an external magnetic field and thermalfluctuation of the magnetization. In case of the discrete pattern in theso-called discrete medium, the influence of the demagnetizing fieldbecomes extremely large as compared with the conventional continuousmedium.

Therefore, when the value of the coercive force squareness ratio S* andthe inequality (2′) are satisfied, although a lower limit value of themagnetization stability becomes smaller as compared with the case of thesaturation magnetization Ms, the coercive force of the medium exceedsthe demagnetizing field caused by the remanent magnetization to therebysuppress age-based reduction in magnetization caused by thermalfluctuation so that the long-term stability is ensured.

On the other hand, as shown in FIG. 4, the length of the sum of L′1 andL′2 is equal to a wavelength of the servo signal recorded herein. L′1and L′2 are generally equal to each other, but a relationship inmagnitude therebetween may be changed depending on the process of signalwaveform processing. That is, since the length of the sum of L′1 and L′2forms one wavelength, it is possible to desirably change one bit lengthdepending on the setting of L′1 and L′2.

In the Gray code area, so-called servo patterns may take various shapescorresponding to sector address numbers (formed by various “0”/“1”patterns) as shown, for example, in a plan view of FIG. 8. That is, theshapes are not limited to the two kinds as described above, i.e. theapproximately rectangular shape (for example, as shown in FIG. 4) andthe belt shape. In case of the pattern shown in FIG. 8, it can bebasically disintegrated into rectangular patterns when seeing theindividual area points, and the present invention may be applied to thedisintegrated patterns.

(2) Description of Second Group in the Invention of First Group

The convex shape of the perpendicular magnetic recording layer 10 in theform of the convex portion that satisfies a required condition of thesecond group corresponds to the shape of the ISG portion 91, the SVAMportion 92, the Gray code portion 93, and the pad portion 95 asdescribed before. As shown in FIG. 5, each of these portions has abelt-like convex portion 10 extending in the track radial direction.This belt-like convex portion 10 has a belt-like shape with a length L′1in the track circumferential direction and a length in the track radialdirection that is 100 times or more the length L′1 as shown in thefigure. When the whole thickness of the magnetic layer in a region ofthe belt-like convex portion is given as t, the interval between themagnetic layers at the belt-like convex portions adjacent to each otherin the track circumferential direction is given as L′2, the thickness ofthe magnetic layer remaining under a region of the concave portion isgiven as δ, and a coercive force, a saturation magnetization, and acoercive force squareness ratio in the direction perpendicular to thefilm plane of the magnetic layer at the belt-like convex portion aregiven as Hc, Ms, and S*, respectively, it is necessary to determine aconfiguration of the belt-like convex portion (including the magneticlayer under the concave portion) and set magnet properties of theperpendicular magnetic recording layer so that the coercive forcesquareness ratio S* takes a value of 0.8 or more and a relationship ofan inequality (3′) below is satisfied, thereby determining aspecification of the belt-like convex portion.

For the respective parameters, the units shown in the tables of thelater-described examples are used. $\begin{matrix}{{{Hc} \cdot S^{*}} > {{Ms}\left( {{4\arctan\frac{L^{\prime}1}{t}} + {4\arctan\frac{L^{\prime}1}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)}} + {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{t}}} \right)}} & \left( 3^{\prime} \right)\end{matrix}$

The expression on the right side of the inequality (3′) represents themagnitude of a demagnetizing field when a saturation magnetization Ms isrecorded at the belt-like convex portion (belt-like elongate rectangularparallelepiped shape) shown in FIG. 5. It has been found that, bysetting a value Hc′ (=Hc·S*), i.e. the product of a coercive force Hcand a coercive force squareness ratio S*, to be greater than a numericalvalue of the demagnetizing field serving to reduce the recordedmagnetization, it is possible to suppress inversion of the magnetizationrecorded at the belt-like convex portion to thereby suppress degradationof a servo signal so that the long-term stability can be achieved.

In this event, as described before, it is necessary that the value ofthe coercive force squareness ratio S* be set to 0.8 or more (preferably0.85 to 1.0, and more preferably 0.9 to 1.0). When the value of thecoercive force squareness ratio S* becomes less than 0.8, the squarenessratio of the M-H curve is decreased, and therefore, there arises adisadvantage that while the demagnetizing field is being applied to themagnetization in the perpendicular magnetic recording layer, themagnetization can be more easily inverted due to an external magneticfield and thermal fluctuation of the magnetization. In case of thediscrete pattern in the so-called discrete medium, the influence of thedemagnetizing field becomes extremely large as compared with theconventional continuous medium.

The magnitudes of the coercive force Hc and the coercive forcesquareness ratio S* can be changed by selection of a material of themagnetic recording layer, an underfilm, a film formation technique, orthe like.

When deriving the foregoing inequality (3′) using a geometric model ofthe belt-like convex portion shown in FIG. 5, the points considered arebasically the same as those in case of deriving the foregoing inequality(1′) except that since the belt-like convex portion has the belt-likeshape with the length L′1 in the track circumferential direction and thelength in the track radial direction that is 100 times or more thelength L′1, there exist many terms that can be approximated to zero. Asa result, there is obtained the inequality (3′) as given above, which issimple.

Further, when a remanent magnetization of the convex-portionperpendicular magnetic recording layer 10 is given as Mr, it isnecessary to determine a configuration of the belt-like convex portion(including the magnetic layer under the concave portion) and set magnetproperties of the perpendicular magnetic recording layer so that arelationship of an inequality (4′) below is satisfied, therebydetermining a specification of the belt-like convex portion. For therespective parameters, the units shown in the tables of thelater-described examples are used.

The points considered when deriving the inequality (4′) were the same asthose in case of the inequality (3′). $\begin{matrix}{{{Hc} \cdot S^{*}} > {{Mr}\left( {{4\arctan\frac{L^{\prime}1}{t}} + {4\arctan\frac{L^{\prime}1}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)}} + {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{t}}} \right)}} & \left( 4^{\prime} \right)\end{matrix}$

The expression on the right side of the inequality (4′) represents themagnitude of a demagnetizing field in the state where saturationrecording is carried out and the magnetization becomes a remanentmagnetization Mr at the belt-like convex portion shown in FIG. 5. It hasbeen found that, by setting a value Hc′ (=Hc·S*), i.e. the product of acoercive force Hc and a coercive force squareness ratio S*, to begreater than a numerical value of the demagnetizing field serving toreduce the recorded magnetization, it is possible to suppress inversionof the magnetization recorded at the convex portion to thereby suppressdegradation of a servo signal caused by a reduction in recordingmagnetization so that the long-term stability can be achieved.

In this event, as described before, it is necessary that the value ofthe coercive force squareness ratio S* be set to 0.8 or more (preferably0.85 to 1.0, and more preferably 0.9 to 1.0). When the value of thecoercive force squareness ratio S* becomes less than 0.8, the squarenessratio of the M-H curve is decreased, and therefore, there arises adisadvantage that while the demagnetizing field is being applied to themagnetization in the perpendicular magnetic recording layer, themagnetization can be more easily inverted due to an external magneticfield and thermal fluctuation of the magnetization. In case of thediscrete pattern in the so-called discrete medium, the influence of thedemagnetizing field becomes extremely large as compared with theconventional continuous medium.

The magnitudes of the coercive force Hc and the coercive forcesquareness ratio S* can be changed by selection of a material of themagnetic recording layer, an underfilm, a film formation technique, orthe like.

Therefore, when the value of the coercive force squareness ratio S* andthe inequality (4′) are satisfied, although a lower limit value of themagnetization stability becomes smaller as compared with the case of thesaturation magnetization Ms, the coercive force of the medium exceedsthe demagnetizing field caused by the residual magnetization to therebysuppress age-based reduction in magnetization caused by thermalfluctuation so that the long-term stability is ensured.

On the other hand, as shown in FIG. 5, the length of the sum of L′1 andL′2 is equal to a wavelength of the servo signal recorded herein. L′1and L′2 are generally equal to each other, but a relationship inmagnitude therebetween may be changed depending on the process of signalwaveform processing. That is, since the length of the sum of L′1 and L′2forms one wavelength, it is possible to desirably change one bit lengthdepending on the setting of L′1 and L′2.

With respect to each of the foregoing perpendicular magnetic recordinglayers of the rectangular parallelepiped shapes, since the demagnetizingfield caused by the recording magnetization is more decreased in theshape with its upper-side corners being rounded as compared with theshape with its upper-side corners not rounded, the long-term stabilitycan be achieved even with the shape with its upper-side corners beingrounded if the foregoing relational expressions are substantiallysatisfied.

The recording of the servo signals in the servo areas in the presentinvention is carried out at a time through saturation magnetization byplacing the perpendicular magnetic recording medium 10 in a DC magneticfield and applying a magnetic field, having an intensity equal to orgreater than an external magnetic field Hn in the magnetization-magneticfield curve shown in FIG. 7, perpendicular to the plane of theperpendicular magnetic recording layers. Therefore, the perpendicularmagnetic recording layers of the data information recording portions(so-called data areas) and the tracking servo information portions(so-called servo areas) are all saturation-magnetized uniformly in acertain direction.

In the servo information portion of the discrete medium of the presentinvention, the demagnetizing field from the adjacent bit is small butnot completely zero. Therefore, it is desirable to adopt a value Hc′(=Hc·S*), i.e. the product of a coercive force Hc and a coercive forcesquareness ratio S*, which is further greater than the isolated bit.

Hereinbelow, specific examples in the invention of the first group willbe shown to thereby describe the present invention in more detail.

(Structure of Magnetic Recording Medium)

As shown in FIG. 1, the disk surface was divided into sectors and, forapplying the sector servo system, servo areas 90 each as shown in FIG. 2were formed. That is, an ISG portion 91, an SVAM portion 92, a Gray codeportion 93, a burst portion 94, and a pad portion 95 were formedaccording to respective servo signal patterns.

Each of convex portions of the burst portion 94 for recording burstsignals was formed as a perpendicular magnetic recording layer having arectangular parallelepiped shape as shown in FIG. 4. Convex portions inthe ISG portion 91, the SVAM portion 92, the Gray code portion 93, andthe pad portion 95 other than the burst portion 94 were, as shown inFIG. 5, each formed as a belt-like convex-portion perpendicular magneticrecording layer having a belt-like rectangular parallelepiped shapeelongate in the disk radial direction and were arranged at intervals ofone bit.

As shown in FIG. 3, the section shape of the medium was such that a PtMnlayer as an orientation layer 14 (underlayer 14) was formed to athickness of 15 nm on a mirror-polished glass substrate 15, a softmagnetic layer 11 made of CoZrNb was formed to a thickness of 200 nm onthe layer 14, and an intermediate layer 12 made of Ru was further formedto a thickness of 8 nm on the layer 11. Subsequently, a perpendicularmagnetic recording layer was formed to a thickness t of 15 nm on thelayer 12, then etching with a predetermined pattern was carried out forforming a predetermined convex-concave shape to thereby obtain convexperpendicular magnetic recording layers 10. The magnetic layer under theconcave portion (residual magnetic layer) was left at a thickness δ of 6mm.

Then, SiO₂ was sputtered to fill etched concave portions. Thereafter,oblique ion-beam etching was carried out while rotating the mediumfilled with SiO₂, thereby removing excessive SiO₂ formed on theperpendicular magnetic recording layers 10 to flatten the surface of themedium. A protective layer 13 in the form of a carbon thin film wasformed to a thickness of 4 nm on the flattened surface of the medium bythe CVD method, and a Fomblin lubricant was further applied to athickness of 1 nm onto the protective layer 13, thereby completing amedium sample. For the perpendicular magnetic recording layer, use wasmade of a material in which CoPt ferromagnetic grains were contained ina matrix in SiO₂.

The recording density of a servo signal was set to 130K·FRPI (FluxReversal Per Inch). Therefore, values of L′1 and L′2 in FIGS. 4 and 5were set to 195 nm, respectively.

Further, the track pitch of a data area was set to 85 nm correspondingto 298.8K·TPI (Track Per Inch). The length W′1 in the track widthdirection and the burst interval W′2 in the track width directioncorresponding to the burst pattern shown in FIG. 4 were set to 85 nm,respectively.

The perpendicular magnetic recording medium subjected to theconvex-concave processing for the servo areas and data areas was, formagnetizing the convex-portion perpendicular magnetic recording layersthat produce servo signal magnetic fields, placed between magnetic polesof an electromagnet where a DC magnetic field of 15 kOe (1193 kA/m) wasgenerated so that the disk surfaces were set parallel to the magneticpole surfaces, and then the perpendicular magnetic recording layers(magnetic layers) in the servo areas and data areas were magnetized at atime to thereby record servo signals.

The magnetic properties of the medium were measured using a vibratingsample magnetometer (VSM). For the coercive force Hc and the coerciveforce squareness ratio S*, use was made of numerical values, correctedby a demagnetizing field, of a non-processed magnetic recording layerafter film formation. This is because, in case of the perpendicularmagnetic recording medium, a strong demagnetizing field is generatedwhen magnetization is carried out in the direction perpendicular to thefilm plane of the medium, so that the magnetization M—magnetic field Hcurve changes due to a change in film thickness and so forth. Thesaturation magnetization Ms and the residual saturation magnetization Mrwere Ms=360 emu/cc (360 kA/m) and Mr=350 emu/cc (350 kA/m).

In order to examine age-based changes of the servo signals of themagnetized perpendicular magnetic recording medium, reproducing GMRheads were set on track in the burst portion, the ISG portion, the SVAMportion, and the Gray code portion to measure age-based changes inreproduction output, respectively.

The track width of each reproducing GMR head was set to 85 nm. Themeasurement of the age-based changes in reproduction output was startedby the GMR heads immediately after the magnetization by the use of anelectromagnet. Thereafter, the measurement was continuously carried outfor three months to measure the changes of the reproduction outputs.

The measurement was carried out by classifying test specifications intothe following four types and description thereof will be givenindividually.

(Test Specification 1-1)

In Examples, Comparative Examples, and Reference Examples shown in Table1 below, the recording density of a servo signal was set to 130K·FRPI(Flux Reversal Per Inch) as described above. The values of L′1 and L′2shown in FIGS. 4 and 5 representing the embodiment of the presentinvention were set to 195 nm, respectively. As described above, thetrack pitch of the data area was set to 85 nm corresponding to298.8K·TPI (Track Per Inch). Further, as described above, the lengthsW′1 and W′2 corresponding to the burst pattern shown in FIG. 4 were setto 85 nm, respectively.

The reproduction output changes of the GMR head were measured bychanging parameters of the perpendicular magnetic recording layercorresponding to the burst pattern of the servo area in FIG. 4 andvalues of the coercive force Hc and the coercive force squareness ratioS* in the direction perpendicular to the film plane of the perpendicularmagnetic recording layer. The values of the coercive force Hc and thecoercive force squareness ratio S* were changed by changing theunderfilm condition and the film deposition method of the magneticrecording layer.

In the reproducing output change, “x” was assigned to a reduction by 10%or more from the initial output after the lapse of three months, while“0” was assigned to a reduction by less than 10%. As an accelerationtest, using the medium that exhibits KuV/kT=80 at 70° C. which is higherthan an ordinary maximum keeping temperature of 60° C., the measurementwas carried out under the condition of KuV/kT=70 at a keepingtemperature of 80° C.

In order to make clear the effect of the relational expressions of thepresent invention, Table 1 simultaneously shows signs of “Hc-α” and“Hc′-α” where a represents the expression on the right side of theforegoing inequality (1′), and values of the coercive force squarenessratio S*. Hc′=Hc·S* and α is given by an equation (5′) below.$\begin{matrix}{\alpha = {{Ms}\left( {{4\arctan\quad\frac{L^{\prime}1\quad W^{\prime}1}{t\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + t^{2}}}} - {4\arctan\quad\frac{L^{\prime}1\quad W^{\prime}2}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}2^{2}} + t^{2}}}} + {4\arctan\quad\frac{L^{\prime}1\quad W^{\prime}1}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{\quad{L^{\prime}1\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} - {4\arctan\frac{\quad{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}}{\left( {t - {2\delta}} \right)\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{\quad{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}}{t\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + t^{2}}}}} \right)}} & \left( 5^{\prime} \right)\end{matrix}$ TABLE 1 Reproduction L′1 L′2 W′1 W′2 δ Ms Hc Output (nm)(nm) (nm) (nm) (nm) (emu/cc) (Oe) Hc-α Hc′-α S* Change Example I-1-1 195195 85 85 6 360 4250 Positive Positive 1.0 ◯ Example I-1-2 195 195 85 856 360 4158 Positive Positive 1.0 ◯ Example I-1-3 195 195 85 85 6 3604387 Positive Positive 0.95 ◯ Example I-1-4 195 195 85 85 6 360 4631Positive Positive 0.90 ◯ Example I-1-5 195 195 85 85 6 360 4915 PositivePositive 0.85 ◯ Example I-1-6 195 195 85 85 6 360 5223 Positive Positive0.80 ◯ Comparative 195 195 85 85 6 360 4148 0 (Zero) 0 (Zero) 1.0 XExample I-1-1 Comparative 195 195 85 85 6 360 4334 Positive Negative0.95 X Example I-1-2 Comparative 195 195 85 85 6 360 4576 PositiveNegative 0.90 X Example I-1-3 Comparative 195 195 85 85 6 360 4845Positive Negative 0.85 X Example I-1-4 Comparative 195 195 85 85 6 3605148 Positive Negative 0.80 X Example I-1-5 Comparative 195 195 85 85 6360 5571 Positive Positive 0.75 X Example I-1-6 Comparative 195 195 8585 6 360 5491 Positive Negative 0.75 X Example I-1-7*Values of demagnetizing fields of samples in Example I-1-1 toComparative Example I-1-7 are all 4148(Oe).

As seen from the results shown in Table 1, it has been confirmed that,in the perpendicular magnetic recording layer satisfying “Hc′-α>0”, i.e.the relationship given by the inequality (1′), and further satisfying“S*≧0.8”, the demagnetization is suppressed even under the conditionthat is more severe than the ordinary keeping condition so that theeffect of the present invention can be achieved. On the other hand, whenS*=0.75, the coercive force increases while the squareness ratio (Mr/Ms)decreases, and the expected property cannot be obtained.

In Table 1, the magnitude of each demagnetizing field is, as understoodfrom “Hc-α=0” when S*=1, 4148 Oe (330 kA/m).

(Test Specification 1-2)

As shown in Table 2 below, the reproduction output changes were measuredusing perpendicular magnetic recording mediums of the magnetic layerstructure formed by the convex-concave pattern which were the same asthose in Test Specification 1-1 while keeping them at the ordinarymaximum keeping temperature of 60° C. Under this condition, KuV/kT=93.3.

In order to make clear the effect of the relational expressions of thepresent invention, Table 2 simultaneously shows signs of “Hc-β” and“Hc′-β” where β represents the expression on the right side of theforegoing inequality (2′), and values of the coercive force squarenessratio S*. Hc′=Hc·S* and β is given by an equation (6′) below.$\begin{matrix}{\beta = {{Mr}\left( {{4\arctan\quad\frac{L^{\prime}1\quad W^{\prime}1}{t\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + t^{2}}}} - {4\arctan\quad\frac{L^{\prime}1\quad W^{\prime}2}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}2^{2}} + t^{2}}}} + {4\arctan\quad\frac{L^{\prime}1\quad W^{\prime}1}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{\quad{L^{\prime}1\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} - {4\arctan\frac{\quad{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}}{\left( {t - {2\delta}} \right)\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{\quad{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}}{t\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + t^{2}}}}} \right)}} & \left( 6^{\prime} \right)\end{matrix}$ TABLE 2 Reproduction L′1 L′2 W′1 W′2 δ Mr Hc Output (nm)(nm) (nm) (nm) (nm) (emu/cc) (Oe) Hc-β Hc′-β S* Change Example I-2-1 195195 85 85 6 350 4200 Positive Positive 1.0 ◯ Example I-2-2 195 195 85 856 350 4043 Positive Positive 1.0 ◯ Example I-2-3 195 195 85 85 6 3504277 Positive Positive 0.95 ◯ Example I-2-4 195 195 85 85 6 350 4514Positive Positive 0.90 ◯ Example I-2-5 195 195 85 85 6 350 4780 PositivePositive 0.85 ◯ Example I-2-6 195 195 85 85 6 350 5073 Positive Positive0.80 ◯ Comparative 195 195 85 85 6 350 4033 0 (Zero) 0 (Zero) 1.0 XExample I-2-1 Comparative 195 195 85 85 6 350 4214 Positive Negative0.95 X Example I-2-2 Comparative 195 195 85 85 6 350 4448 PositiveNegative 0.90 X Example I-2-3 Comparative 195 195 85 85 6 350 4709Positive Negative 0.85 X Example I-2-4 Comparative 195 195 85 85 6 3505004 Positive Negative 0.80 X Example I-2-5 Comparative 195 195 85 85 6350 5424 Positive Positive 0.75 X Example I-2-6 Comparative 195 195 8585 6 350 5337 Positive Negative 0.75 X Example I-2-7*Values of demagnetizing fields of samples in Example I-2-1 toComparative Example I-2-7 are all 4033(Oe).

As seen from the results shown in Table 2, it has been confirmed that,in the perpendicular magnetic recording layer satisfying “Hc′-β>0”, i.e.the relationship given by the equation (6′), and further satisfying“S*≧0.8”, the demagnetization is suppressed even under the condition ofthe ordinary maximum keeping temperature so that the effect of thepresent invention can be achieved. On the other hand, when S*=0.75, thecoercive force increases while the squareness ratio (Mr/Ms) decreases,and the expected property cannot be obtained.

(Test Specification 1-3)

The reproduction output changes of the GMR heads were measured bychanging parameters of the magnetic layer (perpendicular magneticrecording layer) formed by the convex-concave pattern corresponding tothe ISG portion, the SVAM portion, the Gray code portion, or the like inthe servo area as shown in FIG. 5 and values of the coercive force Hcand the coercive force squareness ratio S* in the directionperpendicular to the film plane of the perpendicular magnetic recordinglayer. The results are shown in Table 3 below.

The standard of the reproduction output change was such that, like inTest Specification 1-1, “x” was assigned to a reduction by 10% or morefrom the initial output after the lapse of three months, while “O” wasassigned to a reduction by less than 10%. As an acceleration test, usingthe medium that exhibits KuV/kT=80 at 70° C. which is higher than anordinary maximum keeping temperature of 60° C., the measurement wascarried out under the condition of KuV/kT=70 at 80° C.

In order to make clear the effect of the relational expressions of thepresent invention, Table 3 simultaneously shows signs of “Hc-γ” and“Hc′-γ” where γ represents the expression on the right side of theforegoing inequality (3′), and values of the coercive force squarenessratio S*. Hc′=Hc·S* and γ is given by an equation (7′) below.$\begin{matrix}{\gamma = {{Ms}\left( {{4\arctan\quad\frac{L^{\prime}1}{t}} + {4\arctan\quad\frac{L^{\prime}1}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)}} + {4\arctan\quad\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{t}}} \right)}} & \left( 7^{\prime} \right)\end{matrix}$ TABLE 3 Reproduction L′1 L′2 δ Ms Hc Output (nm) (nm) (nm)(emu/cc) (Oe) Hc-γ Hc′-γ S* Change Example I-3-1 195 195 6 360 4450Positive Positive 1.0 ◯ Example I-3-2 195 195 6 360 4370 PositivePositive 1.0 ◯ Example I-3-3 195 195 6 360 4592 Positive Positive 0.95 ◯Example I-3-4 195 195 6 360 4882 Positive Positive 0.90 ◯ Example I-3-5195 195 6 360 5132 Positive Positive 0.85 ◯ Example I-3-6 195 195 6 3605493 Positive Positive 0.80 ◯ Comparative 195 195 6 360 4362 0 (Zero) 0(Zero) 1.0 X Example I-3-1 Comparative 195 195 6 360 4560 PositiveNegative 0.95 X Example I-3-2 Comparative 195 195 6 360 4813 PositiveNegative 0.90 X Example I-3-3 Comparative 195 195 6 360 5096 PositiveNegative 0.85 X Example I-3-4 Comparative 195 195 6 360 5415 PositiveNegative 0.80 X Example I-3-5 Comparative 195 195 6 360 5816 PositivePositive 0.75 X Example I-3-6 Comparative 195 195 6 360 5776 PositiveNegative 0.75 X Example I-3-7*Values of demagnetizing fields of samples in Example I-3-1 toComparative Example I-3-7 are all 4362(Oe).

As seen from the results shown in Table 3, it has been confirmed that,in the perpendicular magnetic recording layer satisfying “Hc′-γ>0”, i.e.the relationship given by the equation (7′), and further satisfying“S*≧0.8”, the demagnetization is suppressed even under the conditionthat is more severe than the ordinary keeping condition so that theeffect of the present invention can be achieved. On the other hand, whenS*=0.75, the coercive force increases while the squareness ratio (Mr/Ms)decreases, and the expected property cannot be obtained.

In Table 3, the magnitude of each demagnetizing field is, as understoodfrom “Hc-α=0” when S*=1, 4362 Oe (347 kA/m).

(Test Specification 1-4)

As shown in Table 4 below, the reproduction output changes were measuredusing perpendicular magnetic recording mediums of the magnetic layerstructure formed by the convex-concave pattern which were the same asthose in Test Specification 1-3 while keeping them at the ordinarymaximum keeping temperature of 60° C. Under this condition, KuV/kT=93.3.

In order to make clear the effect of the relational expressions of thepresent invention, Table 4 simultaneously shows signs of “Hc-ε” and“Hc′-ε” where E represents the expression on the right side of theforegoing inequality (4′), and values of the coercive force squarenessratio S*. Hc′=Hc·S* and ε is given by an equation (8′) below.$\begin{matrix}{ɛ = {{Mr}\left( {{4\arctan\quad\frac{L^{\prime}1}{t}} + {4\arctan\quad\frac{L^{\prime}1}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)}} + {4\arctan\quad\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{t}}} \right)}} & \left( 8^{\prime} \right)\end{matrix}$ TABLE 4 Reproduction L′1 L′2 δ Mr Hc Output (nm) (nm) (nm)(emu/cc) (Oe) Hc-ε Hc′-ε S* Change Example I-4-1 195 195 6 350 4350Positive Positive 1.0 ◯ Example I-4-2 195 195 6 350 4275 PositivePositive 1.0 ◯ Example I-4-3 195 195 6 350 4496 Positive Positive 0.95 ◯Example I-4-4 195 195 6 350 4746 Positive Positive 0.90 ◯ Example I-4-5195 195 6 350 5024 Positive Positive 0.85 ◯ Example I-4-6 195 195 6 3505339 Positive Positive 0.80 ◯ Comparative 195 195 6 350 4241 0 (Zero) 0(Zero) 1.0 X Example I-4-1 Comparative 195 195 6 350 4433 PositiveNegative 0.95 X Example I-4-2 Comparative 195 195 6 350 4673 PositiveNegative 0.90 X Example I-4-3 Comparative 195 195 6 350 4954 PositiveNegative 0.85 X Example I-4-4 Comparative 195 195 6 350 5264 PositiveNegative 0.80 X Example I-4-5 Comparative 195 195 6 350 5695 PositivePositive 0.75 X Example I-4-6 Comparative 195 195 6 350 5615 PositiveNegative 0.75 X Example I-4-7*Values of demagnetizing fields of samples in Example I-4-1 toComparative Example I-4-7 are all 4241(Oe).

As seen from the results shown in Table 4, it has been confirmed that,in the perpendicular magnetic recording layer satisfying “Hc′-ε>0”, i.e.the relationship given by the equation (8′), and further satisfying“S*≧0.8”, the demagnetization is suppressed even under the condition ofthe ordinary maximum keeping temperature so that the effect of thepresent invention can be achieved. On the other hand, when S*=0.75, thecoercive force increases while the squareness ratio (Mr/Ms) decreases,and the expected property cannot be obtained.

The effects of the present invention are clear from the foregoingresults in the invention of the first group. Specifically, the magneticrecording and reproducing apparatus of the present invention isconfigured such that the specification of the convex structure (themagnetic layer formed by the convex-concave pattern), where the servosignal is recorded, of the perpendicular magnetic recording medium isset according to the properties of the perpendicular magnetic recordingmedium to be used, so that the influence of the demagnetizing field thataccelerates the thermal fluctuation of the perpendicular magneticrecording medium can be reduced in the servo area of the medium which ismost affected by the thermal fluctuation of the medium. Therefore, it ispossible to suppress degradation of the servo signal caused by thethermal fluctuation of the magnetization of the perpendicular magneticrecording layer of the convex-concave structure in the servo area tothereby ensure the stable servo function over the long term.

The magnetic recording and reproducing apparatus of the presentinvention is particularly used as a component of a computer and can beutilized in the apparatus industry for information recording.

Now, description will be given in detail about an embodiment of theinvention of the second group.

[Description About the Invention of Second Group]

Hereinbelow, description will be given in detail about the best mode forcarrying out the invention of the second group (corresponding to FIGS. 9to 16).

A magnetic recording and reproducing apparatus of the present inventioncomprises a magnetic recording medium having data information recordingportions and servo information portions for tracking, and a magnetichead for detecting servo information of the servo information portionsand recording and reproducing data information on and from the datainformation recording portions.

At the outset, an example of a schematic structure of the magneticrecording and reproducing apparatus will be described with reference toFIG. 14 in order to understand the overall structure of the apparatus.

Description of Example of Schematic Structure of Magnetic Recording andReproducing Apparatus

FIG. 14 is a perspective view showing a schematic structure of themagnetic recording and reproducing apparatus being one preferred exampleof the present invention.

In this figure, a magnetic recording medium 1 is a disk-shapedperpendicular magnetic recording medium and is rotationally driven by aspindle motor 2.

Further, in order to read and write data relative to the magneticrecording medium, a recording and reproducing magnetic head 5 isprovided at the tip of a swing arm 4 extending radially inward towardthe center of the medium from its outer peripheral side. The swing arm 4is swung by a voice coil motor 3 so that, for example, the magnetic head5 can be positioned at a given track based on servo signals detected bythe magnetic head 5.

The magnetic head 5 has a recording element and a reproducing element. Asingle-pole head of a main-pole excitation type, for example, is used asthe recording element, while, a GMR (Giant MagnetoResistance effect)head, for example, is used as the reproducing element. A TMR (TunnelingMagnetoResistance effect) head or the like may be used instead of theGMR head.

Description of Magnetic Recording Medium

Now, the structure of the magnetic recording medium will be described.

FIG. 9 is a schematic plan view showing the overall shape of thedisk-shaped magnetic recording medium 1 used in the present invention,and FIG. 10 is an enlarged schematic view of a small portion 100surrounded by a rectangle in FIG. 9. FIG. 10 conceptually illustratesmainly a servo information portion 90 being an area where servo signalsare recorded, and data information recording portions 80 each in theform of a group of data tracks for recording and reproduction.

FIG. 11 is a sectional view conceptually illustrating a preferredembodiment of the magnetic recording medium in the present invention.FIG. 11 substantially corresponds to a sectional view taken along linea-a in FIG. 10.

In FIG. 9, although not illustrated, a plurality of data track groupsfor recording and reproduction are concentrically disposed/formed on adisk substrate.

Further, servo signal regions (servo information portions 90: thoseportions drawn as radial lines in FIG. 9) are radially formed extendingoutward from the center of the disk. That is, a so-called sector servosystem is employed wherein the disk surface is divided into sectors.Servo information is recorded in each of the servo information portions90 of the magnetic recording medium.

The structure of the servo information portion 90 will be described indetail. As shown in FIG. 10, the servo information portion 90 (so-calledservo area) comprises an ISG (Initial Signal Gain) portion 91, an SVAM(SerVo Address Mark) portion 92, a Gray code portion 93, a burst portion94, and a pad portion 95.

The ISG portion 91 is in the form of a continuous pattern provided forexcluding influences of unevenness in magnetic property of a magneticfilm (magnetic layer) of the magnetic recording medium and in flyingamount of the magnetic head and is continuously formed in the trackradial direction. While reproducing the ISG portion 91 by the magnetichead, the gain of a servo demodulation circuit is determined by anautomatic gain control (AGC) so as to correct variation in output causedby the magnetic recording medium or the magnetic head. The automaticgain control (AGC) that performs such an operation is turned off whenthe SVAM portion 92 existing in the servo area is detected, andstandardizes the reproduction amplitude existing in the later burstportion 94 by the amplitude of the ISG portion 91.

The Gray code portion 93 is recorded with information about respectivetrack numbers and a sector number.

The burst portion 94 is in the form of patterns for providing preciseposition information necessary for the magnetic head to perform accuratetracking to the track position. These patterns are normally composed ofa combination of first bursts 94 a and second bursts 94 b each equallystraddling a center line that defines the track pitch between theadjacent tracks and a combination of third bursts 94 c and fourth bursts94 d each located at a position offset from the first and second burstsby half the track pitch. As shown in FIG. 10, the patterns of the burstportion 94 are each normally recorded with a width equal to that of onetrack in a radial direction of the magnetic recording medium.

The pad portion 95 is in the form of a pattern provided for absorbing adelay of a demodulation circuit system so that clock generation can bemaintained while the servo demodulation circuit reproduces the servoarea.

The ISG portion 91, the SVAM portion 92, and the pad portion 95 are eachrecorded continuously in the disk radial direction, while, the Gray codeportion 93 is recorded over several tracks or more in the disk radialdirection.

Referring now to FIG. 11, description will be given about an example ofa preferred section structure of the magnetic recording medium. FIG. 11can be understood as, for example, the sectional view taken along linea-a in FIG. 10.

As shown in FIG. 11, the magnetic recording medium comprises a substrate15, an orientation layer 14 formed on the substrate 15, a soft magneticlayer 11 formed on the orientation layer 14, an intermediate layer 12formed on the soft magnetic layer 11, perpendicular magnetic recordinglayers 10 and nonmagnetic layers 20 corresponding to convex portions andconcave portions, respectively, of the convex-concave shape formed onthe intermediate layer 12, and a protective layer 13 formed on thelayers 10 and 20. In the formation of the convex-concave pattern informing the perpendicular magnetic recording layers 10 of the presentinvention, the magnetic layer is not completely removed in the depthdirection so that the magnetic layer remains at a thickness of about δunder the concave portions (residual magnetic layers 10 a).

Specifically, the servo information portion in the present invention isformed by a convex pattern (perpendicular magnetic recording layers 10)of the magnetic layer formed in the predetermined convex-concavepattern, and a nonmagnetic material is filled inside a concave pattern.

The ratio (δ/t) of the thickness δ of the residual magnetic layer 10 aremaining under the concave portion relative to a thickness t of theperpendicular magnetic recording layer 10 corresponding to the magneticlayer at the convex portion is set to 0.6 or less, preferably 0.1 to0.6, and more preferably 0.2 to 0.4. If this value exceeds 0.6 (thegroove becomes shallow), magnetization becomes liable to be recorded atthe concave portion due to a magnetic field from a recording head and anundesired magnetic field becomes strong from the once-recordedmagnetization so that a noise component increases. On the other hand, ifthis value becomes less than 0.1 (the groove becomes deep), it becomesdifficult to perform predetermined accurate etching and further itbecomes extremely difficult to perform filling of the nonmagneticmaterial and flattening of the surface after the formation of thegroove, resulting in difficulty of stable manufacture.

As the substrate 15, use is preferably made of a glass substrate, anNiP-coated aluminum alloy substrate, an Si substrate, or the like. Asthe orientation layer 14, use can be made of, for example, anantiferromagnetic material such as PtMn for applying an anisotropicmagnetic field to the soft magnetic layer 11 in the track widthdirection. Alternatively, use may be made of a nonmagnetic alloy forcontrolling the orientation.

As the soft magnetic layer 11, there can be cited a CoZrNb alloy, anFe-based alloy, a Co-based amorphous alloy, a soft magnetic/nonmagneticmultilayer film, soft magnetic ferrite, or the like.

The intermediate layer 12 is provided for controlling a perpendicularmagnetic anisotropy and a crystal grain size of the perpendicularmagnetic recording layers formed on the intermediate layer 12, and aCoTi nonmagnetic alloy or Ru, for example, is used therefor.Alternatively, use may be made of a nonmagnetic metal, an alloy, or alow-permeability alloy that works similarly.

As the convex-portion perpendicular magnetic recording layer 10(including the residual magnetic layer 10 a), use is preferably made ofa medium in which ferromagnetic grains of CoPt or the like are containedin a matrix in an SiO₂ oxide-based material, a CoCr-based alloy, an FePtalloy, a Co/Pd-based artificial lattice type multilayer alloy, or thelike.

As a material of the concave-portion nonmagnetic layer 20, use is madeof a nonmagnetic oxide such as SiO₂, Al₂O₃, TiO₂, or ferrite, a nitridesuch as AlN, or a carbide such as SiC.

Normally, the protective layer 13 in the form of a carbon thin film orthe like is formed on the surfaces of the convex-portion perpendicularmagnetic recording layers 10 and the nonmagnetic layers 20 filled in theconcave portions by the use of the CVD method or the like.

The formation of the perpendicular magnetic recording layers 10 and thenonmagnetic layers 20 based on the convex-concave pattern (the formationof the so-called discrete type medium) is carried out by, for example,etching a perpendicular magnetic recording layer, formed in a constantthickness, into a predetermined convex-concave shape, then sputteringSiO₂ corresponding to an etching depth to fill etched concave portions.Thereafter, SiO₂ excessively deposited on the perpendicular magneticrecording layer is removed by applying oblique ion-beam etching or thelike while rotating the medium, thereby flattening the whole surface ofthe medium.

Setting of Specification of Servo Area (Servo Information Portion)

It can be said that the main part of the present invention resides inthat a specification of configuration and magnetic property of aconvex-concave magnetic layer of a perpendicular magnetic recordingmedium is set so as to suppress degradation of a servo signal to therebyensure a stable servo function over the long term in a servo area (servoinformation portion) formed by a convex pattern of the convex-concavemagnetic layer which is formed in a predetermined convex-concave pattern(the magnetic layer of a so-called inner excavation type).

Hereinbelow, with respect to the magnetic recording layers (magneticlayers) having the convex structures for the respective functions in theservo area, description will be separately given about (1) the burstportion 94 (94 a to 94 d) forming a first group that requiresconsideration of lengths in both the track radial direction (disk radialdirection) and the track circumferential direction and (2) the ISGportion 91, the SVAM portion 92, the Gray code portion 93, and the padportion 95 forming a second group that requires consideration of lengthsonly in the track circumferential direction because lengths in the trackradial direction (disk radial direction) are extremely longer than thelengths in the track circumferential direction.

(1) Description of First Group in the Invention of Second Group

The convex shape satisfying a required condition of the first groupcorresponds to the shape of the burst portion 94 as described before. Asshown in a schematic perspective view of FIG. 12, the burst portion 94is formed by disposing at predetermined positions the perpendicularmagnetic recording layers (magnetic layers) 10 in the form of convexportions where magnetizations of burst signals are recorded in the samedirection, and each perpendicular magnetic recording layer 10 in theform of the convex portion has a first and a second substantiallytrapezoidal shape in the track width direction and in the trackcircumferential direction, respectively (truncated quadrangular pyramidshape).

Further, in the present invention, the residual magnetic layers 10 aremain under the concave portions. The meaning of leaving the residualmagnetic layers 10 a under the concave portions resides in reduction ofprocesses for the processing of the concave portions and reduction ofthe depth of the concave portions which leads to easiness of the surfaceflattening thereafter. However, the depth should be set to a value thatcan prevent a signal from the magnetic layer under the concave portionfrom affecting the servo area or the data area.

Incidentally, illustration of the nonmagnetic layers filled in theconcave portions is omitted in the figure for better understanding ofthe shape of the perpendicular magnetic recording layer 10 in the formof the convex portion.

In the first trapezoidal shape in the track width direction (trackradial direction) which can be seen at the front in FIG. 12, an upperside corresponding to the surface (upper surface) of the perpendicularmagnetic recording layer (magnetic layer) 10 in the form of the convexportion is given as W1, a lower side corresponding to a bottom side ofthe perpendicular magnetic recording layer 10 in the form of the convexportion which is extended to reach a base (a lower side corresponding toa bottom side of the magnetic layer in the form of the convex portiondefined by extending the first trapezoidal shape) is given as W2(W2>W1), and the interval between the adjacent lower sides W2 is givenas W3. In the second trapezoidal shape in the track circumferentialdirection which can be seen on the right and left sides in FIG. 12, anupper side corresponding to the surface (upper surface) of theperpendicular magnetic recording layer (magnetic layer) 10 in the formof the convex portion is given as L1, a lower side corresponding to abottom side of the perpendicular magnetic recording layer 10 in the formof the convex portion which is extended to reach a base (a lower sidecorresponding to a bottom side of the magnetic layer in the form of theconvex portion defined by extending the second trapezoidal shape) isgiven as L2 (L2>L1), and the interval between the adjacent lower sidesL2 is given as L3. Further, the whole thickness of the magnetic layer ina region of the convex portion (including a lower part of the convexshape as shown in FIG. 12) is given as t (a distance from the upper sideto the lower side of the magnetic layer at the convex portion), and thethickness of the magnetic layer remaining under the concave portion(residual magnetic layer 10 a) is given as δ.

Then, when the magnetic properties in a direction perpendicular to thefilm plane of the convex-portion magnetic layer (perpendicular magneticrecording layer 10) are assumed to exhibit an M (magnetization)-H(magnetic field) characteristic as shown in FIG. 15, and a coerciveforce, a saturation magnetization, and a coercive force squareness ratioin the direction perpendicular to the film plane of the convex-portionmagnetic layer (perpendicular magnetic recording layer 10) are given asHc, Ms, and S*, respectively, it is necessary to determine aconfiguration of the convex portion (including the magnetic layer underthe concave portion) and set magnet properties of the perpendicularmagnetic recording layer so that the coercive force squareness ratio S*takes a value of 0.8 or more and a relationship of an inequality (1)below is satisfied, thereby determining a specification of the burstportion.

For the respective parameters, units shown in tables of later-describedexamples are used.

The coercive force squareness ratio S* is a value determined by theslope of a tangent line at a point −Hc of the M-H curve shown in FIG. 15which has been corrected by a demagnetizing field, and a value of Mr,and is defined as S*=Hc′/Hc. Hc′ represents a value of the coerciveforce at a point of intersection between the tangent line at the point−Hc of the M-H curve and a straight line of M=Mr in the second quadrantas shown in FIG. 15. Note that “corrected by a demagnetizing field”represents that an applied magnetic field is corrected, with respect toa value of magnetization caused by the applied magnetic field, by theuse of a demagnetizing field generated by the product of themagnetization and a demagnetizing field coefficient in the directionperpendicular to the perpendicular magnetic recording layer, therebyderiving the M-H curve. $\begin{matrix}{{{Hc} \cdot S^{*}} > {{Ms}\left\{ {{4\arctan\frac{{L1}\quad{W1}}{t\sqrt{{L1}^{2} + {W1}^{2} + t^{2}}}} + {4\arctan\frac{\left( {\left( {{{tL}\quad 2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\quad\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{tL2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\quad\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} - {4\arctan\frac{\left( {\left( {{{tL}\quad 2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)\left( {{- {tW2}} + {\delta\quad\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{tL2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{tW2} - {\delta\quad\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} + {4\arctan\frac{\left( {\left( {{{tL}\quad 2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\quad\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{tL2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\quad\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} - {4\arctan\frac{\left( {\left( {{t\left( {{L\quad 2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} + {4\arctan\frac{\left( {{L2} + {2{L3}}} \right)\left( {{W2} + {2{W3}}} \right)}{t\sqrt{\left( {{L2} + {2{L3}}} \right)^{2} + \left( {{W2} + {2{W3}}} \right)^{2} + t^{2}}}}} \right\}}} & (1)\end{matrix}$

The expression on the right side of the inequality (1) represents themagnitude of a demagnetizing field when a saturation magnetization Ms isrecorded at the magnetic layer of the truncated quadrangular pyramidshape formed by the convex-concave pattern shown in FIG. 12. It has beenfound that, by setting a value Hc′ (=Hc·S*), i.e. the product of acoercive force Hc and a coercive force squareness ratio S*, to begreater than a numerical value of the demagnetizing field serving toreduce the recorded magnetization, it is possible to suppress inversionof the magnetization recorded at the convex portion to thereby suppressdegradation of a servo signal so that the long-term stability can beachieved.

In this event, it is necessary that the value of the coercive forcesquareness ratio S* be set to 0.8 or more (preferably 0.85 to 1.0, andmore preferably 0.9 to 1.0). When the value of the coercive forcesquareness ratio S* becomes less than 0.8, the squareness ratio of theM-H curve is decreased, and therefore, there arises a disadvantage thatwhile the demagnetizing field is being applied to the magnetization inthe perpendicular magnetic recording layer, the magnetization can bemore easily inverted due to an external magnetic field and thermalfluctuation of the magnetization. In case of the discrete pattern in theso-called discrete medium, the influence of the demagnetizing fieldbecomes extremely large as compared with the conventional continuousmedium.

The magnitudes of the coercive force Hc and the coercive forcesquareness ratio S* can be changed by selection of a material of themagnetic recording layer, an underfilm, a film formation technique, orthe like.

Further, by forming the convex portion into the truncated quadrangularpyramid shape, the demagnetizing field can be reduced as compared withthe rectangular-type convex-concave structure, and therefore, it becomeseasy to realize the setting specification that can more manifest theeffect of the present invention. Therefore, the effect for extremelyhigh magnetization stability can be manifested by carrying out thesetting so as to form the convex portion into the truncated quadrangularpyramid shape and satisfy the dimensions and magnetic properties of theconvex portion according to the foregoing relational expression (1).

Herein, the length of L2 is set to a bit length corresponding to afrequency of the burst patterns, and L1 is set smaller than L2.Normally, W1 corresponds to the track width of the perpendicularmagnetic recording medium. By setting the section shapes of the convexportion in the track width direction and in the track circumferentialdirection to the trapezoidal shapes, respectively, it is possible tomore reduce the demagnetizing field as compared with therectangular-type convex-concave structure. This is because, since thearea of the perpendicular magnetic recording layer surface correspondingto the upper sides is reduced, the demagnetizing field decreasesfollowing it. In the trapezoidal shape in the present invention, a baseangle θ is set in the range of 55° to 85°, preferably 65° to 80°.Incidentally, in case of the rectangular shape, a base angle θ is 90°.

When deriving the foregoing inequality (1) using a geometric model ofthe trapezoidal convex shape shown in FIG. 12, the following points wereconsidered.

Specifically, in case of the discrete medium, the adjacent bits areisolated from each other as different from the continuous medium, andtherefore, the value of the demagnetizing field Hd was derived withrespect to a demagnetizing field in one specific pattern. In order toderive the representative magnitude, the demagnetizing field was derivedby superimposing, at the center of the truncated quadrangular pyramidshaped structure, magnetic fields generated from magnetic chargesinduced by a perpendicular magnetization M at upper and lower surfacesof the pattern and magnetic fields generated from upper and lowersurfaces of the magnetic layer located under the concave portions (fourportions along the sides of the convex portion) innerly excavated so asto surround the truncated quadrangular pyramid shaped structure of theconvex portion.

Further, when a residual magnetization of the magnetic layer formed bythe convex-concave pattern is given as Mr, it is necessary to determinea configuration of the magnetic layer formed by the convex-concavepattern and set magnet properties of the perpendicular magneticrecording layer so that a relationship of an inequality (2) below issatisfied, thereby determining a specification of the burst portion withrespect to the magnetic layer formed by the convex-concave pattern whichis the same as that in the inequality (1).

For the respective parameters, the units shown in the tables of thelater-described examples are used.

The points considered when deriving the inequality (2) are the same asthose in case of the inequality (1). $\begin{matrix}{{{Hc} \cdot S^{*}} > {{Mr}\left\{ {{4\arctan\frac{{L1}\quad{W1}}{t\sqrt{{L1}^{2} + {W1}^{2} + t^{2}}}} + {4\arctan\frac{\left( {{{tL}\quad 2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\quad\left( {{W2} - {W1}} \right)}} \right)}{t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{tL2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\quad\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}}} - {4\arctan\frac{\left( {{{tL}\quad 2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)\left( {{- {tW2}} + {\delta\quad\left( {{W2} - {W1}} \right)}} \right)}{t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{tL2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{tW2} - {\delta\quad\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}}} + {4\arctan\frac{\left( {{{tL}\quad 2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\quad\left( {{W2} - {W1}} \right)}} \right)}{t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{tL2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\quad\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}}} - {4\arctan\frac{\left( {{t\left( {{L\quad 2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)}{t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}}} + {4\arctan\frac{\left( {{L2} + {2{L3}}} \right)\left( {{W2} + {2{W3}}} \right)}{t\sqrt{\left( {{L2} + {2{L3}}} \right)^{2} + \left( {{W2} + {2{W3}}} \right)^{2} + t^{2}}}}} \right\}}} & (2)\end{matrix}$

The expression on the right side of the inequality (2) represents themagnitude of a demagnetizing field in the state where saturationrecording is carried out and the magnetization becomes a residualmagnetization Mr at the convex-portion magnetic layer of the truncatedquadrangular pyramid shape formed by the convex-concave pattern shown inFIG. 12. It has been found that, by setting a value Hc′ (=Hc·S*), i.e.the product of a coercive force Hc and a coercive force squareness ratioS*, to be greater than a numerical value of the demagnetizing fieldserving to reduce the recorded magnetization, it is possible to suppressinversion of the magnetization recorded at the convex-portion magneticlayer to thereby suppress degradation of a servo signal caused by areduction in recording magnetization so that the long-term stability canbe achieved.

In this event, as described before, it is necessary that the value ofthe coercive force squareness ratio S* be set to 0.8 or more (preferably0.85 to 1.0, and more preferably 0.9 to 1.0). When the value of thecoercive force squareness ratio S* becomes less than 0.8, the squarenessratio of the M-H curve is decreased, and therefore, there arises adisadvantage that while the demagnetizing field is being applied to themagnetization in the perpendicular magnetic recording layer, themagnetization can be more easily inverted due to an external magneticfield and thermal fluctuation of the magnetization. In case of thediscrete pattern in the so-called discrete medium, the influence of thedemagnetizing field becomes extremely large as compared with theconventional continuous medium.

Therefore, when the value of the coercive force squareness ratio S* andthe inequality (2) are satisfied, although a lower limit value of themagnetization stability becomes smaller as compared with the case of thesaturation magnetization Ms, the coercive force of the medium exceedsthe demagnetizing field caused by the residual magnetization to therebysuppress age-based reduction in magnetization caused by thermalfluctuation so that the long-term stability is ensured.

On the other hand, as shown in FIG. 12, the length of the sum of L2 andL3 is equal to a wavelength of the servo signal recorded herein. L2 andL3 are generally equal to each other, but a relationship in magnitudetherebetween may be changed depending on the process of signal waveformprocessing. That is, since the length of the sum of L2 and L3 forms onewavelength, it is possible to desirably change one bit length dependingon the setting of L2 and L3.

In the Gray code area, so-called servo patterns may take various shapescorresponding to sector address numbers (formed by various “0”/“1”patterns) as shown, for example, in a plan view of FIG. 16. That is, theshapes are not limited to the two kinds as described above, i.e. theapproximately rectangular shape (for example, as shown in FIG. 12) andthe belt shape. In case of the pattern shown in FIG. 16, it can bebasically disintegrated into rectangular patterns when seeing theindividual area points, and the present invention may be applied to thedisintegrated patterns.

(2) Description of Second Group in the Invention of Second Group

The convex shape of the perpendicular magnetic recording layer 10 in theform of the convex portion that satisfies a required condition of thesecond group corresponds to the shape of the ISG portion 91, the SVAMportion 92, the Gray code portion 93, and the pad portion 95 asdescribed before. As shown in FIG. 13, each of these portions has abelt-like convex portion 10 extending in the track width direction(track radial direction).

The belt-like convex portion 10 has a trapezoidal shape, in the trackcircumferential direction, with an upper side L1 corresponding to thesurface (upper surface) of the magnetic layer in the form of the convexportion and a lower side L2 (L2>L1) corresponding to a bottom side ofthe magnetic layer in the form of the convex portion which is extendedto reach a base (a lower side corresponding to a bottom side of themagnetic layer in the form of the convex portion defined by extendingthe trapezoidal shape) and has a length in the track width direction(track radial direction) which is 100 times or more the length of L2.

Further, when the interval between the lower sides L2 of the adjacentbelt-like convex portions 10 is given as L3, the whole thickness of themagnetic layer in a region of the convex portion (the distance from theupper side to the lower side of the magnetic layer at the convexportion) is given as t, the thickness of the magnetic layer remainingunder the concave portion is given as δ, and a coercive force, asaturation magnetization, and a coercive force squareness ratio in thedirection perpendicular to the film plane of the magnetic layer at thebelt-like convex portion are given as Hc, Ms, and S*, respectively, itis necessary to determine a configuration of the belt-like convexportion (including the magnetic layer under the concave portion) and setmagnet properties of the perpendicular magnetic recording layer so thatthe coercive force squareness ratio S* takes a value of 0.8 or more anda relationship of an inequality (3) below is satisfied, therebydetermining a specification of the belt-like convex portion.

For the respective parameters, the units shown in the tables of thelater-described examples are used. $\begin{matrix}{{{Hc} \cdot S^{*}} > {{Ms}\left\{ {{4\arctan\frac{L1}{t}} + {4\arctan\frac{{tL2} - {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{\left( {{tL2} + {2{L3}}} \right) + {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} + {4\arctan\frac{{L2} + {2{L3}}}{t}}} \right\}}} & (3)\end{matrix}$

The expression on the right side of the inequality (3) represents themagnitude of a demagnetizing field when a saturation magnetization Ms isrecorded at the belt-like convex portion (belt-like elongate truncatedquadrangular pyramid shape) shown in FIG. 13. It has been found that, bysetting a value Hc′ (=Hc·S*), i.e. the product of a coercive force Hcand a coercive force squareness ratio S*, to be greater than a numericalvalue of the demagnetizing field serving to reduce the recordedmagnetization, it is possible to suppress inversion of the magnetizationrecorded at the belt-like convex portion to thereby suppress degradationof a servo signal so that the long-term stability can be achieved.

In this event, as described before, it is necessary that the value ofthe coercive force squareness ratio S* be set to 0.8 or more (preferably0.85 to 1.0, and more preferably 0.9 to 1.0). When the value of thecoercive force squareness ratio S* becomes less than 0.8, the squarenessratio of the M-H curve is decreased, and therefore, there arises adisadvantage that while the demagnetizing field is being applied to themagnetization in the perpendicular magnetic recording layer, themagnetization can be more easily inverted due to an external magneticfield and thermal fluctuation of the magnetization. In case of thediscrete pattern in the so-called discrete medium, the influence of thedemagnetizing field becomes extremely large as compared with theconventional continuous medium.

The magnitudes of the coercive force Hc and the coercive forcesquareness ratio S* can be changed by selection of a material of themagnetic recording layer, an underfilm, a film formation technique, orthe like.

Further, by forming the belt-like convex portion into the truncatedquadrangular pyramid shape, the demagnetizing field can be reduced ascompared with the rectangular-type convex-concave structure, andtherefore, it becomes easy to realize the setting specification that canmore manifest the effect of the present invention. Therefore, the effectfor extremely high magnetization stability can be manifested by carryingout the setting so as to form the belt-like convex portion into thetruncated quadrangular pyramid shape and satisfy the dimensions andmagnetic properties of the convex portion according to the foregoingrelational expression (3).

When deriving the foregoing inequality (3) using a trapezoidal convexgeometric model being the belt-like convex portion shown in FIG. 13, thepoints considered are basically the same as those in case of derivingthe foregoing inequality (1) except that since the belt-like convexportion has the belt-like shape with the length L1 in the trackcircumferential direction and the length in the track radial directionthat is 100 times or more the length L1, there exist many terms that canbe approximated to zero. As a result, there is obtained the inequality(3) as given above, which is simple.

Further, when a residual magnetization of the convex-portionperpendicular magnetic recording layer 10 is given as Mr, it isnecessary to determine a configuration of the belt-like convex portion(including the magnetic layer under the concave portion) and set magnetproperties of the perpendicular magnetic recording layer so that arelationship of an inequality (4) below is satisfied, therebydetermining a specification of the belt-like convex portion with respectto the truncated quadrangular pyramid shape which is the same as that inthe inequality (3).

For the respective parameters, the units shown in the tables of thelater-described examples are used.

The points considered when deriving the inequality (4) were the same asthose in case of the inequality (3). $\begin{matrix}{{{Hc} \cdot S^{*}} > {{Mr}\left\{ {{4\arctan\frac{L1}{t}} + {4\arctan\frac{{tL2} - {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{\left( {{tL2} + {2{L3}}} \right) + {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} + {4\arctan\frac{{L2} + {2{L3}}}{t}}} \right\}}} & (4)\end{matrix}$

The expression on the right side of the inequality (4) represents themagnitude of a demagnetizing field in the state where saturationrecording is carried out and the magnetization becomes a residualmagnetization Mr at the belt-like convex portion shown in FIG. 13. Ithas been found that, by setting a value Hc′ (=Hc·S*), i.e. the productof a coercive force Hc and a coercive force squareness ratio S*, to begreater than a numerical value of the demagnetizing field serving toreduce the recorded magnetization, it is possible to suppress inversionof the magnetization recorded at the convex portion to thereby suppressdegradation of a servo signal caused by a reduction in recordingmagnetization so that the long-term stability can be achieved.

In this event, it is necessary that the value of the coercive forcesquareness ratio S* be set to 0.8 or more (preferably 0.85 to 1.0, andmore preferably 0.9 to 1.0). When the value of the coercive forcesquareness ratio S* becomes less than 0.8, the squareness ratio of theM-H curve is decreased, and therefore, there arises a disadvantage thatwhile the demagnetizing field is being applied to the magnetization inthe perpendicular magnetic recording layer, the magnetization can bemore easily inverted due to an external magnetic field and thermalfluctuation of the magnetization. In case of the discrete pattern in theso-called discrete medium, the influence of the demagnetizing fieldbecomes extremely large as compared with the conventional continuousmedium.

The magnitudes of the coercive force Hc and the coercive forcesquareness ratio S* can be changed by selection of a material of themagnetic recording layer, an underfilm, a film formation technique, orthe like.

Therefore, when the value of the coercive force squareness ratio S* andthe inequality (4) are satisfied, although a lower limit value of themagnetization stability becomes smaller as compared with the case of thesaturation magnetization Ms, the coercive force of the medium exceedsthe demagnetizing field caused by the residual magnetization to therebysuppress age-based reduction in magnetization caused by thermalfluctuation so that the long-term stability is ensured.

On the other hand, as shown in FIG. 13, the length of the sum of L2 andL3 is equal to a wavelength of the servo signal recorded herein. L2 andL3 are generally equal to each other, but a relationship in magnitudetherebetween may be changed depending on the process of signal waveformprocessing. That is, since the length of the sum of L2 and L3 forms onewavelength, it is possible to desirably change one bit length dependingon the setting of L2 and L3.

With respect to each of the foregoing perpendicular magnetic recordinglayers of the trapezoidal convex shapes, since the demagnetizing fieldcaused by the recording magnetization is more decreased in the shapewith its upper-side corners being rounded as compared with the shapewith its upper-side corners not rounded, the long-term stability can beachieved even with the shape with its upper-side corners being roundedif the foregoing relational expressions are substantially satisfied.

The recording of the servo signals in the servo areas in the presentinvention is carried out at a time through saturation magnetization byplacing the perpendicular magnetic recording medium 10 in a DC magneticfield and applying a magnetic field, having an intensity equal to orgreater than an external magnetic field Hn in the magnetization-magneticfield curve shown in FIG. 15, perpendicular to the plane of theperpendicular magnetic recording layers. Therefore, the perpendicularmagnetic recording layers of the data information recording portions(so-called data areas) and the tracking servo information portions(so-called servo areas) are all saturation-magnetized uniformly in acertain direction.

In the servo information portion of the discrete medium of the presentinvention, the demagnetizing field from the adjacent bit is small butnot completely zero. Therefore, it is desirable to adopt a value Hc′(=Hc·S*), i.e. the product of a coercive force Hc and a coercive forcesquareness ratio S*, which is further greater than the isolated bit.

Hereinbelow, specific examples in the invention of the second group willbe shown to thereby describe the invention of the second group in moredetail.

(Structure of Magnetic Recording Medium)

As shown in FIG. 9, the disk surface was divided into sectors and, forapplying the sector servo system, servo areas 90 each as shown in FIG.10 were formed. That is, an ISG portion 91, an SVAM portion 92, a Graycode portion 93, a burst portion 94, and a pad portion 95 were formedaccording to respective servo signal patterns.

Each of convex portions of the burst portion 94 for recording burstsignals was formed as a perpendicular magnetic recording layer having atruncated quadrangular pyramid shape as shown in FIG. 12. Convexportions in the ISG portion 91, the SVAM portion 92, the Gray codeportion 93, and the pad portion 95 other than the burst portion 94 were,as shown in FIG. 13, each formed as a belt-like convex-portionperpendicular magnetic recording layer having a belt-like truncatedquadrangular pyramid shape elongate in the disk radial direction andwere arranged at intervals of one bit.

As shown in FIG. 11, the section shape of the medium was such that aPtMn layer as an orientation layer 14 (underlayer 14) was formed to athickness of 15 nm on a mirror-polished glass substrate 15, a softmagnetic layer 11 made of CoZrNb was formed to a thickness of 200 nm onthe layer 14, and an intermediate layer 12 made of Ru was further formedto a thickness of 8 nm on the layer 11. Subsequently, a perpendicularmagnetic recording layer was formed to a thickness t of 15 nm on thelayer 12, then etching with a predetermined pattern was carried out forforming a predetermined convex-concave shape to thereby obtain convexperpendicular magnetic recording layers 10. The magnetic layer under theconcave portion (residual magnetic layer) was left at a thickness δ of 6mm.

Then, SiO₂ was sputtered to fill etched concave portions. Thereafter,oblique ion-beam etching was carried out while rotating the mediumfilled with SiO₂′ thereby removing excessive SiO₂ formed on theperpendicular magnetic recording layers 10 to flatten the surface of themedium. A protective layer 13 in the form of a carbon thin film wasformed to a thickness of 4 nm on the flattened surface of the medium bythe CVD method, and a Fomblin lubricant was further applied to athickness of 1 nm onto the protective layer 13, thereby completing amedium sample. For the perpendicular magnetic recording layer, use wasmade of a material in which CoPt ferromagnetic grains were contained ina matrix in SiO₂.

The recording density of a servo signal was set to 130K·FRPI (FluxReversal Per Inch). Therefore, values of L2 and L3 in FIGS. 12 and 13were set to 195 nm, respectively.

Further, the track pitch of a data area was set to 85 nm correspondingto 298.8K·TPI (Track Per Inch). The length W2 in the track widthdirection and the burst interval W3 in the track width directioncorresponding to the burst pattern shown in FIG. 12 were set to 85 nm,respectively.

The perpendicular magnetic recording medium subjected to theconvex-concave processing for the servo areas and data areas was, formagnetizing the convex-portion perpendicular magnetic recording layersthat produce servo signal magnetic fields, placed between magnetic polesof an electromagnet where a DC magnetic field of 15 kOe (1193 kA/m) wasgenerated so that the disk surfaces were set parallel to the magneticpole surfaces, and then the perpendicular magnetic recording layers ofthe truncated quadrangular pyramid shapes in the servo areas and dataareas were magnetized at a time to thereby record servo signals.

The magnetic properties of the medium were measured using a vibratingsample magnetometer (VSM). For the coercive force Hc and the coerciveforce squareness ratio S*, use was made of numerical values, correctedby a demagnetizing field, of a non-processed magnetic recording layerafter film formation. This is because, in case of the perpendicularmagnetic recording medium, a strong demagnetizing field is generatedwhen magnetization is carried out in the direction perpendicular to thefilm plane of the medium, so that the magnetization M—magnetic field Hcurve changes due to a change in film thickness and so forth. Thesaturation magnetization Ms and the residual saturation magnetization Mrwere Ms=360 emu/cc (360 kA/m) and Mr=350 emu/cc (350 kA/m).

In order to examine age-based changes of the servo signals of themagnetized perpendicular magnetic recording medium, reproducing GMRheads were set on track in the burst portion, the ISG portion, the SVAMportion, and the Gray code portion to measure age-based changes inreproduction output, respectively.

The track width of each reproducing GMR head was set to 85 nm. Themeasurement of the age-based changes in reproduction output was startedby the GMR heads immediately after the magnetization by the use of anelectromagnet. Thereafter, the measurement was continuously carried outfor three months to measure the changes of the reproduction outputs.

The measurement was carried out by classifying test specifications intothe following four types and description thereof will be givenindividually.

(Test Specification 2-1)

In Examples, Comparative Examples, and Reference Examples shown in Table5 below, the recording density of a servo signal was set to 130K·FRPI(Flux Reversal Per Inch) as described above. The values of L2 and L3shown in FIGS. 12 and 13 representing the embodiment of the presentinvention were set to 195 nm, respectively. As described above, thetrack pitch of the data area was set to 85 nm corresponding to298.8K·TPI (Track Per Inch). Further, as described above, the lengths W2and W3 corresponding to the burst pattern shown in FIG. 12 were set to85 nm, respectively.

The reproduction output changes of the GMR head were measured bychanging parameters of the perpendicular magnetic recording layer of thetruncated quadrangular pyramid shape corresponding to the burst patternof the servo area in FIG. 12 and values of the coercive force Hc and thecoercive force squareness ratio S* in the direction perpendicular to thefilm plane of the perpendicular magnetic recording layer. The values ofthe coercive force Hc and the coercive force squareness ratio S* werechanged by changing the underfilm condition and the film formationmethod of the magnetic recording layer.

In the reproduction output change, “x” was assigned to a reduction by10% or more from the initial output after the lapse of three months,while “0” was assigned to a reduction by less than 10%. As anacceleration test, using the medium that exhibits KuV/kT=80 at 70° C.which is higher than an ordinary maximum keeping temperature of 60° C.,the measurement was carried out under the condition of KuV/kT=70 at akeeping temperature of 80° C. In order to make clear the effect of therelational expressions of the present invention, Table 5 simultaneouslyshows signs of “Hc-α” and “Hc′-α” where a represents the expression onthe right side of the foregoing inequality (1), and values of thecoercive force squareness ratio S*. Hc′=Hc·S* and a in the invention ofthe second group is given by an equation (5) below. $\begin{matrix}{\alpha = {{Ms}\left\{ {{4\arctan\quad\frac{{L1}\quad{W1}}{t\sqrt{{L1}^{2} + {W1}^{2} + t^{2}}}} + {4\arctan\frac{\left( {\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {{t\left( {t - {2\delta}} \right)}\sqrt{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} - {4\arctan\frac{\left( {\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{- {tW2}} + {\delta\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {{t\left( {t - {2\delta}} \right)}\sqrt{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{tW2} - {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} + {4\arctan\frac{\left( {\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {{t\left( {t - {2\delta}} \right)}\sqrt{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} - {4\arctan\frac{\left( {\left( {{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {{t\left( {t - {2\delta}} \right)}\sqrt{\left( {{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} + {4\arctan\frac{\left( {{L2} + {2{L3}}} \right)\left( {{W2} + {2{W3}}} \right)}{t\sqrt{\left( {{L2} + {2{L3}}} \right)^{2} + \left( {{W2} + {2{W3}}} \right)^{2} + t^{2}}}}} \right\}}} & (5)\end{matrix}$ TABLE 5 Reproduction L1 L2 L3 W1 W2 W3 Ms Hc Output (nm)(nm) (nm) (nm) (nm) (nm) (emu/cc) (Oe) Hc-α Hc′-α S* Change ExampleII-1-1 187 195 195 77 85 85 360 4130 Positive Positive 1.0 ◯ ExampleII-1-2 187 195 195 77 85 85 360 4351 Positive Positive 0.95 ◯ ExampleII-1-3 187 195 195 77 85 85 360 4592 Positive Positive 0.90 ◯ ExampleII-1-4 187 195 195 77 85 85 360 4862 Positive Positive 0.85 ◯ ExampleII-1-5 187 195 195 77 85 85 360 5166 Positive Positive 0.80 ◯Comparative 187 195 195 77 85 85 360 4123 0 (Zero) 0 (Zero) 1.0 XExample II-1-1 Comparative 187 195 195 77 85 85 360 4308 PositiveNegative 0.95 X Example II-1-2 Comparative 187 195 195 77 85 85 360 4548Positive Negative 0.90 X Example II-1-3 Comparative 187 195 195 77 85 85360 4815 Positive Negative 0.85 X Example II-1-4 Comparative 187 195 19577 85 85 360 5116 Positive Negative 0.80 X Example II-1-5 Comparative187 195 195 77 85 85 360 5511 Positive Positive 0.75 X Example II-1-6Comparative 187 195 195 77 85 85 360 5457 Positive Negative 0.75 XExample II-1-7 *Values of demagnetizing fields of samples (samples oftrapezoidal convex portions) in Example II-1-1 to Comparative ExampleII-1-7 are all 4123(Oe). Reference 195 195 195 85 85 85 360 4148 0(Zero) 0 (Zero) 1.0 X Example II-1-1 Reference 195 195 195 85 85 85 3604130 Negative Negative 1.0 X Example II-1-2 Reference 195 195 195 85 8585 360 4351 Positive Negative 0.95 X Example II-1-3 Reference 195 195195 85 85 85 360 4592 Positive Negative 0.90 X Example II-1-4 Reference195 195 195 85 85 85 360 4862 Positive Negative 0.85 X Example II-1-5Reference 195 195 195 85 85 85 360 5166 Positive Negative 0.80 X ExampleII-1-6 *Values of demagnetizing fields of samples (samples ofrectangular convex portions) in Reference Example II-1-1 to ReferenceExample II-1-6 are all 4148(Oe).

As seen from the results shown in Table 5, it has been confirmed that,in the perpendicular magnetic recording layer of the truncatedquadrangular pyramid shape (trapezoidal convex shape) satisfying“Hc′-α>0”, i.e. the relationship given by the inequality (1), andfurther satisfying “S*≧0.8”, the demagnetization is suppressed evenunder the condition that is more severe than the ordinary keepingcondition so that the effect of the present invention can be achieved.On the other hand, when S*=0.75, the coercive force increases while thesquareness ratio (Mr/Ms) decreases, and the expected property cannot beobtained.

In Table 5, the magnitude of each demagnetizing field in the trapezoidalconvex shape is, as understood from “Hc-α=0” when S*=1, 4123 Oe (328kA/m). In contrast, the magnitude of a demagnetizing field in therectangular convex shape shown in each of Reference Examples is 4148 Oe(330 kA/m).

(Test Specification 2-2)

As shown in Table 6 below, the reproduction output changes were measuredusing perpendicular magnetic recording mediums of the magnetic layerstructure formed by the convex-concave pattern which were the same asthose in Test Specification 2-1 while keeping them at the ordinarymaximum keeping temperature of 60° C. Under this condition, KuV/kT=93.3.

In order to make clear the effect of the relational expressions of thepresent invention, Table 6 simultaneously shows signs of “Hc-β” and“Hc′-β” where β represents the expression on the right side of theforegoing inequality (2), and values of the coercive force squarenessratio S*. Hc′=Hc·S* and β in the invention of the second group is givenby an equation (6) below. $\begin{matrix}{\beta = {{Mr}\left\{ {{4\arctan\quad\frac{{L1}\quad{W1}}{t\sqrt{{L1}^{2} + {W1}^{2} + t^{2}}}} + {4\arctan\frac{\left( {\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {{t\left( {t - {2\delta}} \right)}\sqrt{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} - {4\arctan\frac{\left( {\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{- {tW2}} + {\delta\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {{t\left( {t - {2\delta}} \right)}\sqrt{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{tW2} - {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} + {4\arctan\frac{\left( {\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {{t\left( {t - {2\delta}} \right)}\sqrt{\left( {{tL2} - {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} - {4\arctan\frac{\left( {\left( {{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {{t\left( {t - {2\delta}} \right)}\sqrt{\left( {{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} + {4\arctan\frac{\left( {{L2} + {2{L3}}} \right)\left( {{W2} + {2{W3}}} \right)}{t\sqrt{\left( {{L2} + {2{L3}}} \right)^{2} + \left( {{W2} + {2{W3}}} \right)^{2} + t^{2}}}}} \right\}}} & (6)\end{matrix}$ TABLE 6 Reproduction L1 L2 L3 W1 W2 W3 Mr Hc Output (nm)(nm) (nm) (nm) (nm) (nm) (emu/cc) (Oe) Hc-β Hc′-β S* Change ExampleII-2-1 187 195 195 77 85 85 350 4020 Positive Positive 1.0 ◯ ExampleII-2-2 187 195 195 77 85 85 350 4236 Positive Positive 0.95 ◯ ExampleII-2-3 187 195 195 77 85 85 350 4471 Positive Positive 0.90 ◯ ExampleII-2-4 187 195 195 77 85 85 350 4734 Positive Positive 0.85 ◯ ExampleII-2-5 187 195 195 77 85 85 350 5030 Positive Positive 0.80 ◯Comparative 187 195 195 77 85 85 350 4009 0 (Zero) 0 (Zero) 1.0 XExample II-2-1 Comparative 187 195 195 77 85 85 350 4188 PositiveNegative 0.95 X Example II-2-2 Comparative 187 195 195 77 85 85 350 4421Positive Negative 0.90 X Example II-2-3 Comparative 187 195 195 77 85 85350 4681 Positive Negative 0.85 X Example II-2-4 Comparative 187 195 19577 85 85 350 4974 Positive Negative 0.80 X Example II-2-5 Comparative187 195 195 77 85 85 350 5365 Positive Positive 0.75 X Example II-2-6Comparative 187 195 195 77 85 85 350 5305 Positive Positive 0.75 XExample II-2-7 *Values of demagnetizing fields of samples (samples oftrapezoidal convex portions) in Example II-2-1 to Comparative ExampleII-2-7 are all 4009(Oe). Reference 195 195 195 85 85 85 350 4020Negative Negative 1.0 X Example II-2-1 Reference 195 195 195 85 85 85350 4032.4 0 (Zero) 0 (Zero) 1.0 X Example II-2-2 Reference 195 195 19585 85 85 350 4236 Positive Negative 0.95 X Example II-2-3 Reference 195195 195 85 85 85 350 4471 Positive Negative 0.90 X Example II-2-4Reference 195 195 195 85 85 85 350 4734 Positive Negative 0.85 X ExampleII-2-5 Reference 195 195 195 85 85 85 350 5030 Positive Negative 0.80 XExample II-2-6 *Values of demagnetizing fields of samples (samples ofrectangular convex portions) in Reference Example II-2-1 to ReferenceExample II-2-6 are all 4032.4(Oe).

As seen from the results shown in Table 6, it has been confirmed that,in the perpendicular magnetic recording layer of the truncatedquadrangular pyramid shape satisfying “Hc′-β>0”, i.e. the relationshipgiven by the equation (6), and further satisfying “S*≧0.8”, thedemagnetization is suppressed even under the condition of the ordinarymaximum keeping temperature so that the effect of the present inventioncan be achieved. On the other hand, when S*=0.75, the coercive forceincreases while the squareness ratio (Mr/Ms) decreases, and the expectedproperty cannot be obtained.

(Test Specification 2-3)

The reproduction output changes of the GMR heads were measured bychanging parameters of the magnetic layer (perpendicular magneticrecording layer) formed by the convex-concave pattern corresponding tothe ISG portion, the SVAM portion, the Gray code portion, or the like inthe servo area as shown in FIG. 13 and values of the coercive force Hcand the coercive force squareness ratio S* in the directionperpendicular to the film plane of the perpendicular magnetic recordinglayer. The results are shown in Table 7 below.

The standard of the reproduction output change was such that, like inTest Specification 2-1, “x” was assigned to a reduction by 10% or morefrom the initial output after the lapse of three months, while “0” wasassigned to a reduction by less than 10%. As an acceleration test, usingthe medium that exhibits KuV/kT=80 at 70° C. which is higher than anordinary maximum keeping temperature of 60° C., the measurement wascarried out under the condition of KuV/kT=70 at 80° C.

In order to make clear the effect of the relational expressions of thepresent invention, Table 7 simultaneously shows signs of “Hc-γ” and“Hc′-γ” where γ represents the expression on the right side of theforegoing inequality (3), and values of the coercive force squarenessratio S*. Hc′=Hc·S* and γ in the invention of the second group is givenby an equation (7) below. $\begin{matrix}{\gamma = {{Ms}\left\{ {{4\arctan\quad\frac{L1}{t}} + {4\arctan\quad\frac{{tL2} - {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{\quad{{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}}}{\left( {t - {2\delta}} \right)}} + {4\arctan\quad\frac{{L2} + {2{L3}}}{t}}} \right\}}} & (7)\end{matrix}$ TABLE 7 Reproduction L1 L2 L3 Ms Hc Output (nm) (nm) (nm)(emu/cc) (Oe) Hc-γ Hc′-γ S* Change Example II-3-1 187 195 195 360 4450Positive Positive 1.0 ◯ Example II-3-2 187 195 195 360 4633 PositivePositive 0.95 ◯ Example II-3-3 187 195 195 360 4890 Positive Positive0.90 ◯ Example II-3-4 187 195 195 360 5178 Positive Positive 0.85 ◯Example II-3-5 187 195 195 360 5501 Positive Positive 0.80 ◯ Comparative187 195 195 360 4371 0 (Zero) 0 (Zero) 1.0 X Example II-3-1 Comparative187 195 195 360 4569 Positive Negative 0.95 X Example II-3-2 Comparative187 195 195 360 4823 Positive Negative 0.90 X Example II-3-3 Comparative187 195 195 360 5107 Positive Negative 0.85 X Example II-3-4 Comparative187 195 195 360 5426 Positive Negative 0.80 X Example II-3-5 Comparative187 195 195 360 5868 Positive Positive 0.75 X Example II-3-6 Comparative187 195 195 360 5788 Positive Negative 0.75 X Example II-3-7*Values of demagnetizing fields of samples (samples of trapezoidalconvex portions) in Example II-3-1 to Comparative Example II-3-7 are all4371(Oe).

As seen from the results shown in Table 7, it has been confirmed that,in the perpendicular magnetic recording layer of the truncatedquadrangular pyramid shape satisfying “Hc′-γ>0”, i.e. the relationshipgiven by the equation (7), and further satisfying “S*≧0.8”, thedemagnetization is suppressed even under the condition that is moresevere than the ordinary keeping condition so that the effect of thepresent invention can be achieved. On the other hand, when S*=0.75, thecoercive force increases while the squareness ratio (Mr/Ms) decreases,and the expected property cannot be obtained.

(Test Specification 2-4)

As shown in Table 8 below, the reproduction output changes were measuredusing perpendicular magnetic recording mediums of the magnetic layerstructure formed by the convex-concave pattern which were the same asthose in Test Specification 2-3 while keeping them at the ordinarymaximum keeping temperature of 60° C. Under this condition, KuV/kT=93.3.

In order to make clear the effect of the relational expressions of thepresent invention, Table 8 simultaneously shows signs of “Hc-ε” and“Hc′-ε” where ε represents the expression on the right side of theforegoing inequality (4), and values of the coercive force squarenessratio S*. Hc′=Hc·S* and ε in the invention of the second group is givenby an equation (8) below. $\begin{matrix}{ɛ = {{Ms}\left\{ {{4\arctan\quad\frac{L1}{t}} + {4\arctan\quad\frac{{tL2} - {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{\quad{{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}}}{\left( {t - {2\delta}} \right)}} + {4\arctan\quad\frac{{L2} + {2{L3}}}{t}}} \right\}}} & (8)\end{matrix}$ TABLE 8 Reproduction L1 L2 L3 Mr Hc Output (nm) (nm) (nm)(emu/cc) (Oe) Hc-ε Hc′-ε S* Change Example II-4-1 187 195 195 350 4260Positive Positive 1.0 ◯ Example II-4-2 187 195 195 350 4504 PositivePositive 0.95 ◯ Example II-4-3 187 195 195 350 4754 Positive Positive0.90 ◯ Example II-4-4 187 195 195 350 5034 Positive Positive 0.85 ◯Example II-4-5 187 195 195 350 5348 Positive Positive 0.80 ◯ Comparative187 195 195 350 4249 0 (Zero) 0 (Zero) 1.0 X Example II-4-1 Comparative187 195 195 350 4441 Positive Negative 0.95 X Example II-4-2 Comparative187 195 195 350 4688 Positive Negative 0.90 X Example II-4-3 Comparative187 195 195 350 4964 Positive Negative 0.85 X Example II-4-4 Comparative187 195 195 350 5273 Positive Negative 0.80 X Example II-4-5 Comparative187 195 195 350 5705 Positive Positive 0.75 X Example II-4-6 Comparative187 195 195 350 5625 Positive Negative 0.75 X Example II-4-7*Values of demagnetizing fields of samples (samples of trapezoidalconvex portions) in Example II-4-1 to Comparative Example II-4-7 are all4249(Oe).

As seen from the results shown in Table 8, it has been confirmed that,in the perpendicular magnetic recording layer of the truncatedquadrangular pyramid shape satisfying “Hc′-ε>0”, i.e. the relationshipgiven by the equation (8), and further satisfying “S*≧0.8”, thedemagnetization is suppressed even under the condition of the ordinarymaximum keeping temperature so that the effect of the present inventioncan be achieved. On the other hand, when S*=0.75, the coercive forceincreases while the squareness ratio (Mr/Ms) decreases, and the expectedproperty cannot be obtained.

The effects of the invention of the second group are clear from theforegoing results. Specifically, the magnetic recording and reproducingapparatus of the present invention is configured such that thespecification of the convex structure (the magnetic layer formed by theconvex-concave pattern), where the servo signal is recorded, of theperpendicular magnetic recording medium is set according to theproperties of the perpendicular magnetic recording medium to be used, sothat the influence of the demagnetizing field that accelerates thethermal fluctuation of the perpendicular magnetic recording medium canbe reduced in the servo area of the medium which is most affected by thethermal fluctuation of the medium. Therefore, it is possible to suppressdegradation of the servo signal caused by the thermal fluctuation of themagnetization of the perpendicular magnetic recording layer of theconvex-concave structure in the servo area to thereby ensure the stableservo function over the long term.

The magnetic recording and reproducing apparatus of the presentinvention is particularly used as a component of a computer and can beutilized in the apparatus industry for information recording.

1. A magnetic recording and reproducing apparatus comprising a magneticrecording medium having a data information recording portion and a servoinformation portion for tracking, and a magnetic head for detectingservo information of said servo information portion and recording andreproducing data information on and from said data information recordingportion, wherein said servo information portion is formed by a convexpattern of a magnetic layer formed in a predetermined convex-concavepattern and a nonmagnetic material is filled inside a concave pattern,said servo information portion comprising a burst portion where burstsignals for tracking are recorded, said burst portion is formed bydisposing at predetermined positions magnetic layers in the form ofconvex portions where the burst signals are recorded, and when a lengthof said magnetic layer in the form of the convex portion in a trackcircumferential direction is given as L′1, a length thereof in a trackwidth direction (track radial direction) is given as W′1, a wholethickness of said magnetic layer in a region of the convex portion isgiven as t, an interval in the track width direction (track radialdirection) between said magnetic layers in the form of the convexportions adjacent to each other is given as W′2, an interval thereof inthe track circumferential direction is given as L′2, a thickness of themagnetic layer remaining under a concave portion is given as 6, and acoercive force, a saturation magnetization, and a coercive forcesquareness ratio in a direction perpendicular to the film plane of saidmagnetic layer in the form of the convex portion are given as Hc, Ms,and S*, respectively, a specification of said burst portion is set sothat said coercive force squareness ratio S* takes a value of 0.8 ormore and a relationship of a first inequality is satisfied, said firstinequality given as $\begin{matrix}{{{Hc} \cdot S^{*}} > {{Ms}\left( \quad{{4\arctan\frac{L^{\prime}1\quad W^{\prime}1}{t\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + t^{2}}}} - {4\arctan\frac{L^{\prime}1\quad W^{\prime}2}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}2^{2}} + t^{2}}}} + {4\arctan\frac{L^{\prime}1\quad W^{\prime}1}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{L^{\prime}1\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{t\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + t^{2}}}}} \right)}} & \quad\end{matrix}$
 2. A magnetic recording and reproducing apparatusaccording to claim 1, wherein when a coercive force, a residualmagnetization, and a coercive force squareness ratio in the directionperpendicular to the film plane of said magnetic layer in the form ofthe convex portion are given as Hc, Mr, and S*, respectively, thespecification of said burst portion is set so that said coercive forcesquareness ratio S* takes the value of 0.8 or more and a relationship ofa second inequality is satisfied, said second inequality given as$\begin{matrix}{{{Hc} \cdot S^{*}} > {{Mr}\left( \quad{{4\arctan\frac{L^{\prime}1\quad W^{\prime}1}{t\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + t^{2}}}} - {4\arctan\frac{L^{\prime}1\quad W^{\prime}2}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}2^{2}} + t^{2}}}} + {4\arctan\frac{L^{\prime}1\quad W^{\prime}1}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + {W^{\prime}1^{2}} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{L^{\prime}1\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)\sqrt{{L^{\prime}1^{2}} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + \left( {t - {2\delta}} \right)^{2}}}} + {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)\left( {{W^{\prime}1} + {2W^{\prime}2}} \right)}{t\sqrt{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)^{2} + \left( {{W^{\prime}1} + {2W^{\prime}2}} \right)^{2} + t^{2}}}}} \right)}} & \quad\end{matrix}$
 3. A magnetic recording and reproducing apparatusaccording to claim 1, wherein said magnetic layer in the form of theconvex portion has a substantially rectangular parallelepiped shape. 4.A magnetic recording and reproducing apparatus according to claim 1,wherein the sum of said L′1 and L′2 is set as a wavelength of frequencyof a servo signal.
 5. A magnetic recording and reproducing apparatuscomprising a magnetic recording medium having a data informationrecording portion and a servo information portion for tracking, and amagnetic head for detecting servo information of said servo informationportion and recording and reproducing data information on and from saiddata information recording portion, wherein said servo informationportion is formed by a convex pattern of a magnetic layer formed in apredetermined convex-concave pattern and a nonmagnetic material isfilled inside a concave pattern, said servo information portioncomprising belt-like convex portions each extending in a track radialdirection (track width direction), said belt-like convex portion has abelt-like shape having a length L′1 in a track circumferential directionand a length in the track radial direction that is 100 times or more thelength L′1, and when a whole thickness of the magnetic layer in a regionof the belt-like convex portion is given as t, an interval in the trackcircumferential direction between the magnetic layers in the form of thebelt-like convex portions adjacent to each other is given as L′2, athickness of the magnetic layer remaining under a region of a concaveportion is given as δ, and a coercive force, a saturation magnetization,and a coercive force squareness ratio in a direction perpendicular tothe film plane of said magnetic layer in the form of the belt-likeconvex portion are given as Hc, Ms, and S*, respectively, aspecification of said belt-like convex portion is set so that saidcoercive force squareness ratio S* takes a value of 0.8 or more and arelationship of a first inequality is satisfied, said first inequalitygiven as $\begin{matrix}{{{Hc} \cdot S^{*}} > {{Ms}\left( {{4\arctan\frac{L^{\prime}1}{t}} + {4\arctan\frac{L^{\prime}1}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)}} + {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{t}}} \right)}} & \quad\end{matrix}$
 6. A magnetic recording and reproducing apparatusaccording to claim 5, wherein when a coercive force, a residualmagnetization, and a coercive force squareness ratio in the directionperpendicular to the film plane of said magnetic layer are given as Hc,Mr, and S*, respectively, the specification of said belt-like convexportion is set so that said coercive force squareness ratio S* takes thevalue of 0.8 or more and a relationship of a second inequality issatisfied, said second inequality given as $\begin{matrix}{{{Hc} \cdot S^{*}} > {{Mr}\quad\left( {{4\arctan\frac{L^{\prime}1}{t}} + {4\arctan\frac{L^{\prime}1}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{\left( {t - {2\delta}} \right)}} + {4\arctan\frac{\left( {{L^{\prime}1} + {2L^{\prime}2}} \right)}{t}}} \right)}} & \left( 3^{\prime} \right)\end{matrix}$
 7. A magnetic recording and reproducing apparatusaccording to claim 5, wherein said magnetic layer in the form of thebelt-like convex portion has a belt-like rectangular parallelepipedshape.
 8. A magnetic recording and reproducing apparatus according toclaim 5, wherein the sum of said L′1 and L′2 is set as a wavelength offrequency of a servo signal.
 9. A magnetic recording and reproducingapparatus according to claim 1, wherein recording of servo signals insaid servo information portion is carried out at a time by applying amagnetic field perpendicular to the plane of said magnetic layers ofsaid magnetic recording medium in a DC magnetic field.
 10. A magneticrecording and reproducing apparatus comprising a magnetic recordingmedium having a data information recording portion and a servoinformation portion for tracking, and a magnetic head for detectingservo information of said servo information portion and recording andreproducing data information on and from said data information recordingportion, wherein said servo information portion is formed by a convexpattern of a magnetic layer formed in a predetermined convex-concavepattern and a nonmagnetic material is filled inside a concave pattern,said servo information portion comprising a burst portion where burstsignals for tracking are recorded, said burst portion is formed bydisposing at predetermined positions magnetic layers in the form ofconvex portions where the burst signals are recorded, said magneticlayer in the form of the convex portion has a first and a secondsubstantially trapezoidal shape in a track width direction (track radialdirection) and in a track circumferential direction, respectively, andwhen an upper side corresponding to an upper surface of the magneticlayer in the form of the convex portion is given as W1, a lower sidecorresponding to a bottom side of the magnetic layer in the form of theconvex portion which is extended to reach a base (a lower sidecorresponding to a bottom side of the magnetic layer in the form of theconvex portion defined by extending said first trapezoidal shape) isgiven as W2, and an interval between the adjacent lower sides W2 isgiven as W3 with respect to said first trapezoidal shape in the trackwidth direction, an upper side corresponding to the upper surface of themagnetic layer in the form of the convex portion is given as L1, a lowerside corresponding to a bottom side of the magnetic layer in the form ofthe convex portion which is extended to reach a base (a lower sidecorresponding to a bottom side of the magnetic layer in the form of theconvex portion defined by extending said second trapezoidal shape) isgiven as L2, and an interval between the adjacent lower sides L2 isgiven as L3 with respect to said second trapezoidal shape in the trackcircumferential direction, a whole thickness of the magnetic layer in aregion of the convex portion (a distance from the upper side to thelower side of the magnetic layer in the form of the convex portion) isgiven as t, a thickness of the magnetic layer remaining under a concaveportion is given as δ, and a coercive force, a saturation magnetization,and a coercive force squareness ratio in a direction perpendicular tothe film plane of said magnetic layer in the form of the convex portionare given as Hc, Ms, and S*, respectively, a specification of said burstportion is set so that said coercive force squareness ratio S* takes avalue of 0.8 or more and a relationship of a first inequality issatisfied, said first inequality given as${{Hc} \cdot S^{*}} > {{Ms}\left\{ {{4\arctan\frac{{L1}\quad{W1}}{t\sqrt{{L1}^{2} + {W1}^{2} + t^{2}}}} + {4\arctan\frac{\left( {\left( {{{tL}\quad 2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\quad\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{tL2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\quad\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} - {4\arctan\frac{\left( {{{tL}\quad 2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)\left( {{- {tW2}} + {\delta\quad\left( {{W2} - {W1}} \right)}} \right)}{t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{tL2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{tW2} - {\delta\quad\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}}} + {4\arctan\frac{\left( {\left( {{{tL}\quad 2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\quad\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{tL2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\quad\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} - {4\arctan\frac{\left( {\left( {{t\left( {{L\quad 2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)} \right)}{\left( {t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}} \right)}} + {4\arctan\frac{\left( {{L2} + {2{L3}}} \right)\left( {{W2} + {2{W3}}} \right)}{t\sqrt{\left( {{L2} + {2{L3}}} \right)^{2} + \left( {{W2} + {2{W3}}} \right)^{2} + t^{2}}}}} \right\}}$11. A magnetic recording and reproducing apparatus according to claim10, wherein when a coercive force, a residual magnetization, and acoercive force squareness ratio in the direction perpendicular to thefilm plane of said magnetic layer in the form of the convex portion aregiven as Hc, Mr, and S*, respectively, the specification of said burstportion is set so that said coercive force squareness ratio S* takes thevalue of 0.8 or more and a relationship of a second inequality issatisfied, said second inequality given as${{Hc} \cdot S^{*}} > {{Mr}\left\{ {{4\arctan\frac{{L1}\quad{W1}}{t\sqrt{{L1}^{2} + {W1}^{2} + t^{2}}}} + {4\arctan\frac{\left( {{{tL}\quad 2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\quad\left( {{W2} - {W1}} \right)}} \right)}{t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{tL2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} - {W1} - {W3}} \right)} - {\delta\quad\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}}} - {4\arctan\frac{\left( {{{tL}\quad 2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)\left( {{- {tW2}} + {\delta\quad\left( {{W2} - {W1}} \right)}} \right)}{t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{tL2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{tW2} - {\delta\quad\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}}} + {4\arctan\frac{\left( {{{tL}\quad 2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\quad\left( {{W2} - {W1}} \right)}} \right)}{t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{tL2} - {\delta\quad\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\quad\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}}} - {4\arctan\frac{\left( {{t\left( {{L\quad 2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)\left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)}{t\quad\left( {t - {2\delta}} \right)\sqrt{\left( {{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}} \right)^{2} + \left( {{t\left( {{W2} + {2{W3}}} \right)} + {\delta\left( {{W2} - {W1}} \right)}} \right)^{2} + \left( {t\left( {t - {2\delta}} \right)} \right)^{2}}}} + {4\arctan\frac{\left( {{L2} + {2{L3}}} \right)\left( {{W2} + {2{W3}}} \right)}{t\sqrt{\left( {{L2} + {2{L3}}} \right)^{2} + \left( {{W2} + {2{W3}}} \right)^{2} + t^{2}}}}} \right\}}$12. A magnetic recording and reproducing apparatus according to claim10, wherein a relationship of W2>W1 and L2>L1 is satisfied.
 13. Amagnetic recording and reproducing apparatus according to claim 10,wherein the sum of said L2 and L3 is set as a wavelength of frequency ofa servo signal.
 14. A magnetic recording and reproducing apparatuscomprising a magnetic recording medium having a data informationrecording portion and a servo information portion for tracking, and amagnetic head for detecting servo information of said servo informationportion and recording and reproducing data information on and from saiddata information recording portion, wherein said servo informationportion is formed by a convex pattern of a magnetic layer formed in apredetermined convex-concave pattern and a nonmagnetic material isfilled inside a concave pattern, said servo information portioncomprising belt-like convex portions each extending in a track radialdirection (track width direction), said belt-like convex portion has atrapezoidal shape, in a track circumferential direction, with an upperside L1 corresponding to an upper surface of the magnetic layer in theform of the belt-like convex portion and a lower side L2 correspondingto a bottom side of the magnetic layer in the form of the belt-likeconvex portion which is extended to reach a base (a lower sidecorresponding to a bottom side of the magnetic layer in the form of thebelt-like convex portion defined by extending said trapezoidal shape)and has a length in the track radial direction which is 100 times ormore a length of L2, and when an interval between the lower sides L2 ofthe adjacent belt-like convex portions is given as L3, a whole thicknessof the magnetic layer in a region of the belt-like convex portion (adistance from the upper side to the lower side of the magnetic layer inthe form of the belt-like convex portion) is given as t, a thickness ofthe magnetic layer remaining under a concave portion is given as δ, anda coercive force, a saturation magnetization, and a coercive forcesquareness ratio in a direction perpendicular to the film plane of saidmagnetic layer in the form of the belt-like convex portion are given asHc, Ms, and S*, respectively, a specification of said belt-like convexportion is set so that said coercive force squareness ratio S* takes avalue of 0.8 or more and a relationship of a first inequality issatisfied, said first inequality given as${{Hc} \cdot S^{*}} > {{Ms}\left\{ {{4\arctan\frac{L1}{t}} + {4\arctan\frac{{tL2} - {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} + {4\arctan\frac{{L2} + {2{L3}}}{t}}} \right\}}$15. A magnetic recording and reproducing apparatus according to claim14, wherein when a coercive force, a residual magnetization, and acoercive force squareness ratio in the direction perpendicular to thefilm plane of said magnetic layer in the form of the belt-like convexportion are given as Hc, Mr, and S*, respectively, the specification ofsaid belt-like convex portion is set so that said coercive forcesquareness ratio S* takes the value of 0.8 or more and a relationship ofa second inequality is satisfied, said second inequality given as${{Hc} \cdot S^{*}} > {{Mr}\left\{ {{4\arctan\frac{L1}{t}} + {4\arctan\frac{{tL2} - {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} - {4\arctan\frac{{t\left( {{L2} + {2{L3}}} \right)} + {\delta\left( {{L2} - {L1}} \right)}}{\left( {t - {2\delta}} \right)}} + {4\arctan\frac{{L2} + {2{L3}}}{t}}} \right\}}$16. A magnetic recording and reproducing apparatus according to claim14, wherein a relationship of L2>L1 is satisfied.
 17. A magneticrecording and reproducing apparatus according to claim 14, wherein thesum of said L2 and L3 is set as a wavelength of frequency of a servosignal.
 18. A magnetic recording and reproducing apparatus according toclaim 10, wherein recording of servo signals in said servo informationportion is carried out at a time by applying a magnetic fieldperpendicular to the plane of said magnetic layers of said magneticrecording medium in a DC magnetic field.
 19. A magnetic recording andreproducing apparatus according to claim 10, wherein said servoinformation portion is formed in the predetermined convex-concavepattern and the nonmagnetic material for providing a discrete functionis filled in the concave portions.